Libro de texto_Chemistry and Physics 3 ESO

3 ESO

Chemistry and Physics Projecte de Seccions Europees Illes Balears MarĂ­a Paz Terrasa Sagrera

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Edita: EDICIONS TALAIOT, S.L. C. Castelló de la Plana, 30 07181 Palmanova (Calvià) T. 971 75 16 04 edicionstalaiots@gmail.com www.edicionstalaiots.com Autora: María Paz Terrasa Sagrera Il·lustració i maquetació: Sara Socías Impressió: INSTITUT | Imprenta Digital. Palma ISBN 978-84-939484-6-7 D.L. PM-406-2012

3 ESO

Chemistry and Physics Projecte de Seccions Europees Illes Balears MarĂ­a Paz Terrasa Sagrera

Chemistry and Physics 3 ESO is aimed at CLIL students CLIL (Content and Language Integrated Learning) "CLIL refers to situations where subjects, or part of subjects, are taught through a foreign language with dual-focussed aims, namely the learning of content, and the simultaneous learning of a foreign language" (Marsh, 1994) This approach involves learning Chemistry and Physics through an additional language. It can be very successful in enhancing the learning of languages and other subjets, and developing in the youngsters a positive "can do" attitude towards themselves as language learners. (Marsh, 2000) This text is being updated and prepared to help those teachers involved in the experience of implementing bilinguism in European schools and in Spanish schools mainly.

Índice

Unit 1. Science. Measurement.............................................................................9 1 Science definition........................................................................................................... 10 1.1 Chemistry ............................................................................................................... 10 1.2 Physics .................................................................................................................... 10 2. Properties of matter ..................................................................................................... 11 3. Measurement ................................................................................................................ 12 3.1 SI Prefixes Table .................................................................................................... 13 3.2 Changing units and conversion factors .............................................................. 13 4. Measurement instruments.......................................................................................... 14 5. Direct measurements and indirect measurements ................................................. 14 6. Collecting data. Graphs and tables............................................................................. 15 7. The Scientific Method ................................................................................................... 17 7.1 Reasoning in science ............................................................................................. 17 7.2 Questions and answers ........................................................................................ 17 7.3 Experimental evidence ......................................................................................... 17 7.4 The whole process ................................................................................................ 18

Unit 2. States of matter .......................................................................................... 21 1 The kinetic theory of gases ........................................................................................... 22 2. Gases laws ..................................................................................................................... 24 2.1 Boyle's/Mariotte's Law .......................................................................................... 24 2.2 Gay Lussac's Law ................................................................................................... 25 2.3 Charles' Law ........................................................................................................... 26 3. States of matter and kinetic theory ............................................................................ 27 4. Changes of state ........................................................................................................... 28 4.1 Energy Changes Accompanying Changes of State ............................................ 28 4.2 Heating Curves ...................................................................................................... 28 4.3 Kinetic theory and changes of state.................................................................... 30 4.4 Changes of state at different conditions ............................................................ 31

Unit 3. Types of matter ..........................................................................................35 1 Pure substances and mixtures .................................................................................... 36 2 Separating mixtures ...................................................................................................... 38 2.1 By filtering .............................................................................................................. 38 2.2 By centrifuging ....................................................................................................... 38 2.3 By evaporating the solvent .................................................................................. 39 2.4 By cristallising ........................................................................................................ 39 2.5 Cromatography ..................................................................................................... 40 2.6 Distillation .............................................................................................................. 40 2.7 Decanting ............................................................................................................... 41 2.8 By using a magnet ................................................................................................ 41 3. Homogeneous mixtures. Solutions ............................................................................ 42 3.1 Anything can be in solution ................................................................................. 42 3.2 Making Solutions ................................................................................................... 42 3.3 Anything can change solutions ............................................................................ 43 3.4 Concentration of a solution ................................................................................. 43 4. Common substances.................................................................................................... 45 4.1 Dalton´s atomic theory ........................................................................................ 46

Unit 4. The atom ...................................................................................................... 49 1. Electricity ........................................................................................................................ 50 2. The particles of the atom ............................................................................................. 51 2.1 Atoms as Building Blocks ..................................................................................... 51 5

Ă?ndice 3. Atom models ................................................................................................................. 54 3.1 The Thomson model ............................................................................................. 54 3.2 The Rutherford model .......................................................................................... 54 3.3 The size of the atom ............................................................................................. 55 3.4 The Bohr atom model ........................................................................................... 56 4. Atoms, isotopes and ions ............................................................................................ 56 4.2 Ions.......................................................................................................................... 59 4.3 Ion characteristics ................................................................................................. 59 4.4 Electrovalence........................................................................................................ 60 5. Radioactivity .................................................................................................................. 61 5.1 Nuclear fusion ....................................................................................................... 63 5.2 Nuclear fission ....................................................................................................... 63

Unit 5. Elements and compounds....................................................................67 1. Chemical elements ....................................................................................................... 68 2. The Periodic table ......................................................................................................... 69 2.1 The arrangement of the electrons ...................................................................... 69 2.2 How to work out the arrangement of electrons................................................ 70 3. Common chemical elements ................................................................................. 71 4. Atoms, molecules and crystals .................................................................................... 72 4.1 Isolated atoms ....................................................................................................... 72 4.2 Molecules ............................................................................................................... 72 4.3 Crystals ................................................................................................................... 72 4.4 Chemical bonds ..................................................................................................... 73 4.5 Properties of the substances ............................................................................... 74 5. Chemical compounds................................................................................................... 74

Unit 6. Chemical changes .................................................................................... 77 1. Physical and chemical changes ................................................................................... 78 2. Chemical reactions ....................................................................................................... 78 2.1 The signs of a chemical change ........................................................................... 78 2.2 Collision theory ...................................................................................................... 78 3. Mass measurements. The mole.................................................................................. 79 3.1 Molar Mass ............................................................................................................. 79 4. Chemical equations ...................................................................................................... 80 5. Calculations from chemical equations ....................................................................... 82 5.1 What an equation tells us..................................................................................... 82 5.2 Calculations involving only masses ..................................................................... 83 5.3 Calculations involving gas volumes..................................................................... 83

Unit 7. Chemistry beyond the classroom ....................................................87 1. Interesting chemical reactions .................................................................................... 88 1.1 Combustion Reactions.......................................................................................... 88 1.2 Acid base reactions ............................................................................................... 89 1.3 Neutralisation reaction ......................................................................................... 90 2. Chemistry and environment ....................................................................................... 91 2.1 Greenhouse eect................................................................................................. 91 2.2 Acid rain .................................................................................................................. 91 2.3 The ozone layer ..................................................................................................... 91 2.4 Causes of Air Pollution.......................................................................................... 92 2.5 Water pollution ...................................................................................................... 93 3. Drugs .............................................................................................................................. 94 4. Chemistry and social development ............................................................................ 94 4.1 Use of Chemistry in Agriculture:.......................................................................... 94 4.2 Food chemistry ...................................................................................................... 94 6

1

UNIT

Science. Measurement

1. Science definition 2. Properties of matter 3. Measurement 4. Measurement instruments 5. Direct measurements and indirect measurements 6. Collecting data. Graphs and tables 7. The Scientific Method

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1 UNIT Science. Measurement

1 Science definition The word science comes from the Latin "scientia" meaning knowledge.

The definition of science is "knowledge attained through study or practice" or "knowledge covering general truths of the operation of general laws, especially as obtained and tested through scientific method and concerned with the physical world."

What is the purpose of science? Perhaps the most general description is that the purpose of science is to produce useful models of reality.

Most scientific investigations use some form of the scientific method.

Science as defined above is sometimes called pure science to differentiate it from applied science, which is the application of research to human needs. Fields of science are commonly classified along two major lines: • Natural sciences, the study of the natural world • Social sciences, the systematic study of human behaviour and society

1.1 Chemistry Chemistry is the science of matter at or near the atomic scale. Matter is the substance of which all physical objects are made.

Chemistry deals with the properties of matter, and the transformation and interactions of matter and energy.

1.2 Physics Physics is the study of the natural world. It deals with the fundamental particles of which the universe is made. Physics is the science of Nature, of matter and energy in space and time. Physicists study a wide range of physical phenomena as motion or atmosphere and even The Universe. Topics dealing with Physics are the study of motion and forces as well as work or energy. Physics can give answer to questions such us why a boat can float or it could sink. Some of these topics are to be studied next year.

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Science. Measurement UNIT

1

2. Properties of matter Matter is all that has a shape and occupies space. General properties are those that do not let us distinguish among the substances, e.g. volume, mass or temperature.

Characteristic properties have a determined value for each substance and let us dierentiate them. Examples are density, melting and boiling point and solubility.

Density is the relationship between the mass of a body and the volume that it occupies. In mathematics we express the relationship between two properties by dividing them. So, to calculate the density of a body, we use the equation:

d= where

m V

d = density, expressed in kg/mÂł m = mass, in kg V = volume, measured in mÂł

Questions 1. Say whether the following concepts are science or not: a. Astrology b. Astronomy c. X rays and laser d. The genome e. Geology f. Chemistry 2. Explain which of the following concepts are quantities: a. Beauty b. Colour c. Volume d. Temperature e. Price in euros f. The taste g. Smell h. Length

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1 UNIT Science. Measurement

3. Measurement Quantity: It is all that you can measure and express with a number followed by a unit.

Unit: It is what we use to express quantities.

The International System of Units is the modern form of the metric system and is generally a system of units of measurement.

Types of quantities: base quantities measured directly by comparision with the fundamental, and derived quantities, obtained from the base quantities.

Table 1. Base quantities

Table 1. Derived quantities

Quantity

Unit

Quantity

Unit

Length

Length metre (m)

Surface

square meter (m²)

Mass

kilogram (kg)

Volume

cubic meter (m³)

Time

second (s)

Density

kilogram per cubic meter (kg/m³)

Speed

metres per second (m/s)

Temperature

Kelvin (k)

Acceleration

metres per second squared (m/s²)

Amount of substance

mole (mol)

Force

Newton (N)

Electric current

ampere (A)

Energy

Joule (J)

Questions 3. Write down the symbol and the equivalence. For example 1kg = 1000g. a. Milligrams b. Nanoseconds c. Kilolitres d. Micrometres e. Centimetres f. Decimetres g. Millilitres h. Hectometres i. Milliseconds

4. Write down the equivalence of the following measurements in the SI: a. 1 hL b. 30 cm c. 100 mm d. 25 g e. 40 hm f. 25 km g. 80 mg h. 2,5 dm i. 450 mm h. 1000 mL

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Science. Measurement UNIT

1

3.1 SI Prefixes Table The International System of Units, universally abreviated SI is the modern metric system of measurement.

The 20 SI prefixes used to form decimal multiples and submultiples of SI units are: Name

Factor

Symbol

Name

Factor

Y

yotta

1024

y

yokto

10−24

Z

zetta

1021

z

zepto

10−21

E

exa

1018

a

atto

10−18

P

peta

1015

f

femto

10−15

T

tera

1012

p

pico

10−12

G

giga

109

n

nano

10−9

M

mega

106

μ

micro

10−6

K

kilo

103

m

milli

10−3

H

hecto

102

c

centi

10−2

Da

deka

101

d

deci

10−1

3.2 Changing units and conversion factors To change one unit into another it is necessary to use conversion factors. Examples are the conversion from kilometres to metres or hours to seconds.

A conversion factor is a fraction in which numerator and denominator express the same value but in different units. For example: a. The radius of an atom is 0,85 nm. Express it in metres.

0,85 nm

10−9 1 nm

−10

m=8,5.10

m

b. The film last 2 hours. Express this time in seconds.

2h

3600 s

=7200 s 1h Conversion factors allows you to express a result in a different unit from the data given.

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1 UNIT Science. Measurement

4. Measurement instruments In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number attached to a unit.

Examples of instruments for measurement are: atomic clock, chronograph, scales, the ruler, the protactor.

5. Direct measurements and indirect measurements In physics, there are some things that are very easy to measure 'directly.' These are things like weight, distance, or time. So if I wanted to measure how long a piece of wood is, I would just measure how long it is.

But let's say I wanted to find out about something that is a little harder to measure, like how quickly the wind is blowing. I may not be able to measure the wind's actual speed, but if I had a windmill, I could measure how much power the windmill is making. Then, using this information, I could work backwards to figure out how fast the wind must be. This would be an example where I have to measure something 'indirectly.'

Length, mass and time are measured directly by comparing with the instrument of measurement ruler, scales and chronograph respectively.

Speed, acceleration and force are good examples of indirect measurements. We work them out from the measurements of distance moved (length), time and mass.

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Science. Measurement UNIT

1

6. Collecting data. Graphs and tables Tables and graphs are visual representations. They are used to organise information to show patterns and relationships. A graph shows this information by representing it as a shape. Researchers and scientists often use tables and graphs to report findings from their research.

In newspapers, magazine articles, and on television they are often used to support an argument or point of view.

We are going to carry out some activities, to help you understand.

WORKED EXAMPLE 1 A parachutist falls downward from an helicopter. Every second, before opening the parachute, his velocity increases 36 km/h. Draw a graph of the velocity from the first second to the 6s.

Time (s)

1

2

3

4

5

6

Velocity (km/h)

36

72

108

144

180

216

This graph is a straight line. This means that the two quantities time and velocity are direct. An increase in time causes an increase in speed.

13

1 UNIT Science. Measurement WORKED EXAMPLE 2 A balloon is submerged in the sea. The pressure increases as the depth does. The values obtained in an experiment are represented in a table.

1

0,50

0,33

0,25

0,20

Pressure (atm)

1

2

3

4

5

atm

Volume (L)

l

The graph is not a straight line. It means that the two quantities are indirect, the more increases one of them, the more decreases the other one.

Questions 5. If we put a liquid at 20ÂşC into the freezer we observe that every 2 minutes its temperature decreases 3 degrees Celsius. Write down the data of the change in temperature for 10 minutes. Draw a graph of this phenomenon.

6. You are trying to find the relationship between the volume of carbon dioxide produced and the mass of calcium carbonate used.

Mass CaCO3 (g) Vol CO2 (cmÂł)

0,020

0,040

0,060

0,085

0,100

0,120

3

10

13

20

24

31

Plot a graph from the data collected in the table above.

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Science. Measurement UNIT

1

7. The Scientific Method 7.1 Reasoning in science Learning about the scientific method is almost like saying that you are learning how to learn. You see, the scientific method is the way scientists learn and study the world around them. It can be used to study anything from a leaf to a dog to the entire Universe.

The basis of the scientific method is asking questions and then trying to come up with the answers. You could ask, "Why do dogs and cats have hair?" One answer might be that it keeps them warm.

7.2 Questions and answers Just about everything starts with a question. Usually, scientists come up with questions by looking at the world around them.

As more questions are asked, scientists work hard and come up with a bunch of answers. Then it is time to organize. One of the cool things about science is that other scientists can learn things from what has already been established. They do not have to go out and test everything again and again. That is what makes science special: it builds on what has been learned before.

7.3 Experimental evidence Experimental evidence is what makes all of the observations and answers in science valid, truthful or confirmed. The history of evidence and validations show that the original statements were correct and accurate. It sounds like a simple idea, but it is the basis of all science. Statements must be confirmed with loads of evidence.

Scientists start with observations and then make a hypothesis or a guess, and then the fun begins. They must then prove their hypothesis with trials and tests that show why their data and results are correct. They must use controls, which are quantitative based on values and figures, not emotions. Science needs both ideas -the hypothesis- and facts -the quantitative results- to move forward. Scientists can then examine their data and develop newer ideas. This process will lead to more observation and refinement of hypotheses.

15

1 UNIT Science. Measurement 7.4 The whole process There are different terms used to describe scientific ideas based on the amount of confirmed experimental evidence: Hypothesis • A statement that uses a few observations • An idea based on observations without experimental evidence Theory • Uses many observations and has loads of experimental evidence • Can be applied to unrelated facts and new relationships flexible enough to be modified if new data or evidence are introduced Law • Stands the test of time, often without change • Experimentally confirmed over and over • Can create true predictions for different situations • Has uniformity and is universal

You may also hear about the term "model" A model is a scientific statement that has some experimental validity or is a scientific concept that is only accurate under limited situations. Models do not work or apply under all situations in all environments.

They are not universal ideas like a law or theory. In this year, atom models are to be studied.

http://www.sciencebuddies.org/science-fair-projects/project_scientific_method.shtml

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Science. Measurement UNIT

1

Questions 7. Which of the following units are accurate to express a quantity? What is the name of the quantity? a. A pencil b. A 1 euro coin c. A rice grain d. A cup e. One minute f. One ton g. One second h. One kilometre i. A brick of milk 8. Say which type of example is studied in a Physics lesson and which one is studied in a Chemistry lesson: a. A train going down a roller coaster b. The echo produced in a concert c. The melting of ice d. To lit a fire e. An explosion f. Frying an egg g.Working out the speed of a race car h. Measuring the length of a pencil i. Timing a runner j. A metal rusting 9. A piece of matter has a density of 1 g/ml and boils at 100 ºC. By observing the table, say which of the following substances is made up of the piece: oil, gold, water, alcohol, helium.

Substances

Density (g/ml)

Boiling point (ºC)

Helium

0,126

-269

Gold

19,3

2.970

Water

1,0

100

Oil

0,6

220

Alcohol

0,9

78

10. Write down the following lengths from the lowest to the highest: a. 5.10−3 m b. 10−8 m c. 107 m d. 102 m e. 3.106 m f. 2.10−4 m g. 10−5 m

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1 UNIT Science. Measurement Questions 11. Write down the following masses from the lowest to the highest: a. 1024 kg b. 70 kg c. 1000 g d. 600 kg e. 1 mg f. 1 ng g. 1 t 12. Write down in scientific notation the following amounts: a. 300.000 km/s b. 0,004523 kg c. 9798,75 cm d. 10,000.000 m e. 602.200.000.000.000.000.000.000 u f. 0,0000001 m 13. Express the following quantities in S.I. units: a. 154 cm b. 551 dm c. 5 mn d. 0,25 h e 36 km/h f. 1 mm g. 3 h 30 mn h. 10 km i. 3 t j. 540 g 14. Write down the following values of time from the highest to the lowest: a. 3 h 40 min b. 1.800 min c. 120 min d. 2 h 10 min e. 3.600 s f. 760 min g. 1 day 3 h 40 min h. 18 years 9 months 1 day 1 h 1 min i. 4.500 million years 15. Express in scientific notation the following values: a. 0,00023 b. 0,05 c. 0,00000008 d. 0,0001

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2 UNIT

States of matter

1. The kinetic theory of gases 2. Gases laws 3. States of matter and kinetic theory 4. Changes of state

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2 UNIT States of matter

1 The kinetic theory of gases Matter is everything around you. Matter is anything made of atoms and molecules.

Matter is anything that has a mass.

The earth is one large mixture of molecules in gases, liquids and solids

Solids are usually hard because their molecules have been packed together. The closer your molecules are, the harder you are. Solids also can hold their own shape.

A book, a pencil or a key, are examples of solids.

Liquids are an in-between state of matter. They can be found in between the solid and gas states.

One characteristic of a liquid is that it will fill up the shape of a container. If you pour some water in a cup, it will fill up the bottom of the cup first and then fill the rest.

The water will also take the shape.

Another trait of liquids is that they are diďŹƒcult to compress.

Gases can fill a container of any size or shape. That is one of their physical characteristics. Think about a balloon. No matter what shape you make the balloon it will be evenly filled with the gas atoms. The atoms and molecules are spread equally throughout the entire balloon. Liquids can only fill the bottom of the container while gases can fill it entirely.

Gases hold huge amounts of energy, and their molecules are spread out as much as possible. With very little pressure, when compared to liquids and solids, those molecules can be compressed. Combinations of pressure and decreasing temperature force gases into tubes that we use every day. You might see compressed air in a spray bottle or feel the carbon dioxide rush out of a can of soda. Those are both examples of gas forced into a space smaller than it would want, and the gas escapes the first chance it gets.

20

States of matter UNIT 2

In this unit, we will study the gases. It is difficult to know what the amount of gas there is in a container. This is calculated from the quantities volume, temperature and pressure.

Volume of a gas is the same as the volume of the container. It is expressed in litres ( l ) or in cubic metres (m³).

1m

3

3

=1000 dm =1000 litres

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. It is related to the motion of the gas molecules. It is expressed in kelvin (K) or in degrees Celsius (ºC).

T ( K )=T (ºC )+273 The pressure is given by the impacts of moving gas molecules, as they collide with the walls from the inside. It is measured in Pascal (Pa), in millimetres of mercury or in atmospheres (atm).

1 atm=760 mm Hg =101.325 Pa

The kinetic-molecular theory of gases, physical theory that explains the behaviour of gases on the basis of the following assumptions: • Any gas is composed of a very large number of very tiny particles called molecules • The molecules are very far apart compared to their sizes, so that they can be considered as points • The molecules exert no forces on one another except during rare collisions, and these collisions are perfectly elastic, they take place within a negligible span of time and in accordance with the laws of mechanics • Gases exert a pressure inside the container • The faster the molecules, the higher the temperature of the gas

Absolute Zero Absolute zero is the point where no more heat can be removed from a system, according to the absolute temperature scale. This corresponds to 0 K or -273°C. In classical kinetic theory, there should be no movement of individual molecules at absolute zero. Kelvin scale of temperature starts in the absolute zero. There are no lower temperatures from this value.

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2 UNIT States of matter

2. Gases laws When you blow up a balloon, you fill it with air particles moving at speed. The particles knock against the sides of the balloon and exert pressure on it. The pressure is what keeps the balloon inflated. In the same way, all gases exert pressure. This pressure depends on the temperature of the gas and the volume it fills, as you will see below.

2.1 Boyle's/Mariotte's Law Boyle's law states that the volume of a gas decreases when the pressure increases at a constant temperature.

The relationship between the pressure and the volume is expressed by the formula:

P i . V i =P f . V

f

where:

Pi Vi Pf Vf

= Initial Pressure = Initial Volume = Final Pressure = Final Volume

For a given mass, at constant temperature, the pressure times the volume is a constant. pV =C

Kinetic Theory explains Boyle-Mariotte´s experiment. Temperature remains constant. According to kinetic theory, particles move at the same speed all the time.

If the volume decreases, the pressure increases because the particles are closer the walls and the collisions are more frequent. On the other hand, if the volume is increased, the particles have more space to move and there are less collisions, so that the pressure decreases.

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States of matter UNIT 2 WORKED EXAMPLE 1 A certain amount of gas contains a volume of 4 L at 1,2 atm pressure. Find the pressure of the gas if it occupies in 15 L container. P i=1,2 atm , V i =4 L , V f =15 L Substitute the values in the below final pressure equation:

Final Pressure(V f )= Pi V i /V = (1,2 x 4)/ 15 = 4,8 /15

f

Final Pressure(P f )=0,32atm WORKED EXAMPLE 2 Find the final volume of gas, from 8 L of gas at 2 atm until the pressure becomes 3 atm. P i=2 atm , V i =8 L , P f =3 atm .

Substitute the values in the below volume equation:

Final Volume (V f )=P i V i / P f = (2 x 8)/ 3 = 16/ 3

Final Volume (V f )=5,3 L 2.2 Gay Lussac's Law Gay-Lussac's Law states that the pressure of a sample of gas at constant volume, is directly proportional to its temperature in Kelvin.

According to Gay-Lussac's Law:

P 1 /T 1=P 2 / T 2 .

The figure above represents gas molecules at dierent pressure values and the same volume.

23

2 UNIT States of matter 2.3 Charles' Law Assuming that the pressure remains constant, the volume and absolute temperature of a certain quantity of a gas are directly proportional.

Mathematically, this can be represented as: Temperature = Constant x Volume Because the formula is equal to a constant, it is possible to solve for a change in volume or temperature using a proportion:

V 1 /T 1=V 2 /T 2 To explain why this happens, let's explore temperature and volume in terms of gases. Temperature is an average of molecular motion. This means that, while all of the gas molecules are moving around their container in different directions at different speeds, they will have an average amount of energy that is the temperature of the gas.

The volume of the gas is the size of its container because the molecules will move in a straight line until they impact something as another molecule or the container walls. However, to move as they do, the molecules require kinetic energy, which is measured by temperature.

Charles' Law must be used with the Kelvin temperature scale. This scale is an absolute temperature scale. At 0 K, there is no kinetic energy and it is known as Absolute Zero. According to Charles' Law, there would also be no volume at that temperature. This condition cannot be fulfilled because all known gases will liquify or solidify before reaching 0 K. The Kelvin temperature scale is Celsius minus 273°.Therefore, zero Kelvin would be -273º and any Celsius temperature can be converted by to Kelvin by adding 273 .

In the two containers there are the same number of molecules. The pressure is the same, but the more you heat up the gas, the more the volume increases.

24

States of matter UNIT 2

3. States of matter and kinetic theory In the same way that a solid holds its shape, the atoms inside of a solid are not allowed to move around too much. This is one of the physical characteristics of solids. Atoms and molecules in liquids and gases are bouncing and floating around, free to move where they want. The molecules in a solid are stuck. The atoms still spin and the electrons fly around, but the entire atom will not change position.

Density in a solid is larger than in a liquid because particles are closer, and in gases density is lower than in liquids because particles are more separated.

Questions 1. Why is so risky “passive smoking�?

2. The density of a substance is always the same in solid state than in liquid state?

25

2 UNIT States of matter

4. Changes of state In general, matter in one state can be changed into either of the other two states.

To convert a solid into a liquid it is necessary to heat it up so as to pass from liquid to gas. To convert from liquid to solid and from gas to liquid, you need to cool down.

4.1 Energy Changes Accompanying Changes of State Each change of state is accompanied by a change in the energy of the system.Whenever the change involves the disruption of intermolecular forces, energy must be supplied.

The melting process for a solid is also referred to as fusion.

Vaporization requires the input of heat energy.

• Our bodies use this as a mechanism to remove excess heat from ourselves. We sweat, and its evaporation requires heat input as the excess heat from ourselves.

• Refrigerators use the evaporation of Freon (CCl2F2) to remove heat inside the fridge. The Freon is condensed outside the cabinet usually in coils at the back, in a process which releases heat energy. The coils will be warm.

4.2 Heating Curves The heating of ice at -25 °C to +125 °C at a constant pressure of 1 atm will exhibit the following characteristics. The figure represents time in x-axis versus temperature in y-axis.

26

States of matter UNIT 2

During the change of state, the temperature remains constant, as it is observed in the graph above.

Melting point is the temperature at which a substance changes from solid to liquid state. It is the same as the freezing point. For water, melting point is 0ยบC. Boiling point is the temperature at which a substance changes from liquid to gas state. It is just the same as the condensation temperature. Boiling point of water is 100 ยบC. Table 1. Melting and boiling points Substance

Melting point (ยบC)

Boiling point (ยบC)

Water

0

100

Acetone

-94,7

56

Lead

327

1.749

Copper

1.085

2.570

Iron

1.538

2.861

Mercury

-38.9

356.7

Common salt

801

1.465

Nitrogen

-210

-195.8

Oxygen

-218,8

-183

Ammonia

-77,7

-33,3

27

2 UNIT States of matter 4.3 Kinetic theory and changes of state The kinetic theory of matter can be used to explain how solids, liquids and gases are interchangeable as a result of increase or decrease in heat energy. When an object is heated the motion of the particles increases as the particles become more energetic. If it is cooled the motion of the particles decreases as they lose energy.

Melting In a solid the strong attractions between the particles hold them tightly packed together. When a solid is heated the particles gain energy and start to vibrate faster and faster. Initially the structure is gradually weakened which has the eect of expanding the solid.

Further heating provides more energy until the particles start to break free of the structure. Although the particles are still loosely connected they are able to move around. At this point the solid is melting to form a liquid.

The particles in the liquid are the same as in the solid but they have more energy.

To melt a solid energy is required to overcome the attractions between the particles and allow them to pull them apart. The energy is provided when the solid is heated up.

Boiling If a liquid is heated the particles are given more energy and move faster and faster expanding the liquid. The most energetic particles at the surface escape from the surface of the liquid as a vapour as it gets warmer. Liquids evaporate faster as they heat up and more particles have enough energy to break away.

The particles need energy to overcome the attractions between them. As the liquid gets warmer more particles have suďŹƒcient energy to escape from the liquid. Eventually even particles in the middle of the liquid form bubbles of gas in the liquid. At this point the liquid is boiling and turning to gas.

Evaporating Within a liquid some particles have more energy than other. These "more energetic particles" may have suďŹƒcient energy to escape from the surface of the liquid as gas or vapour. This process is called evaporation and the result of evaporation is commonly observed when puddles or clothes dry.

Evaporation takes place at room temperature which is often well below the boiling point of the liquid. Evaporation happens from the surface of the liquid. As the temperature increases the rate of evaporation increases.

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States of matter UNIT 2 Sublimation Some substances can change from solid to gas and vice versa without involving any liquid on the way. This is known as sublimation.

4.4 Changes of state at different conditions Melting and boiling points depend on the conditions. Water boils at 100 ยบC at atmospheric pressure. If the pressure is higher, the boiling point will be higher too, because the particles need more energy to break up and to separate enough to become a liquid.

On the other hand, if the pressure is lower, as in a high mountain water boils at a temperature less than 100ยบC since the particles need less energy to break up. On top of Everest water boils at 70ยบC. In a pressure cooker, water reaches a temperature higher than 100 ยบC before boiling. This is the reason why food is cooked more quickly.

http://www.chem.purdue.edu/gchelp/atoms/states.html

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2 UNIT States of matter Questions 3. Why is a dish dried faster than a glass of water?

4. Explain the reason why you feel less hot a windy day than a smooth calm day despite the fact the room temperature is the same.

5. Convert the centigrade temperatures to the kelvin scale: a. 0 ºC b. 25 ºC c. 27 ºC d. -100 ºC 6. Write down the following pressures in atmospheres: a. 670 mm Hg b. 600 mm Hg c. 700 mm Hg d. 1.045 mm Hg 7. Convert these volumes into cm³: a. 200 mL b. 1 L c. 0,5 L d. 100 m³ 8. Complete the following table by using Boyle´s law P (atm)

1

V (L)

2

2

10 0,25

9. Oxygen gas is introduced in a 5 L container at a pressure of 4 atmospheres.

Which pressure will the gas exert if the container's volume is doubled without a change in temperature?

10. An amount of gas occupies a volume of 5 L when the pressure is 1 atm. Which will the new volume be if the pressure increases to 2 atm and the temperature does not change?

11. In a container of 5 L a gas is introduced at a pressure of 4 atm and its temperature is 27 ºC. Which will the pressure be if the temperature increases to 127 ºC without changing the container's volume?

12. At 0 ºC a gas exerts a pressure of 2 atm. At which temperature will it be found if the pressure is 4 atm and the volume does not change?

13. Which volume will a gas occupy at 300 K if at 250 K occupied 2 L and the pressure does not vary?

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States of matter UNIT 2

Questions 14. Complete the table for Gay-Lussac´s law P (atm) T (K)

1

2

100

8 400

15. Complete the following table and say if the following values at a constant temperature are according to Boyle's law. Draw a graph of pressure against volume.

Answer the questions: a) Which is the pressure if the volume is 0,1 L? b) Which is the volume if the pressure increases to 2 atm?

P (atm)

V(L)

0,10

5,00

0,25

2,00

0,50

1,00

0,75

0,67

1,00

0,50

P·V (atm·L)

16. A gas occupies a volume of 5 L at 0 ºC. Which temperature will it reach if it occupies a volume of 10 litres without changing the pressure?

17. The graph below shows the warming up of a pure substance. a) Identify the changes of state b) Which is the melting point of the substance? c) Which is the boiling point of the substance? d) How long does it take to melt the substance? e) How long does it take to change into vapour f) Which is the state after 5, 25, 50 and 90 minutes heating?

18. Complete the table for Charles´law V (L)

2

T (K)

100

5

48 200

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2 UNIT States of matter Questions

19. Which changes of state take place in the following situations: a. When you smell perfume b. When ice is formed c. When the clothes get dried d. When you dry your hair 20. The table below shows the temperature of a liquid heating curve for 10 minutes.

Time (min)

0

2

4

6

8

10

Temperature (ºC)

20

30

40

50

50

50

a. Draw a graph temperature-time b. Which is the boiling point of the liquid? c. Which is the condensation point?

21. Say if the following sentences are true or false: a. When heating a liquid an increase in temperature is not always produced. b. Water boils at 100 ºC everywhere around the world.

22. Say which of the following sentences are true: a. When a substance changes its state it is converted into another substance. b. An increase in temperature takes place in every change of state. c. If we warm up a solid substance we will be able to melt it. d. It is necessary to reach a temperature of 100 ºC for the water to change from liquid to solid state.

23. What does it mean the fact that the boiling point of the alcohol is 78 ºC? a. That the temperature at which it melts is 78 ºC b. That the alcohol boils at temperatures below 78 ºC c. That the alcohol passes from liquid to gas at 78 ºC d. That the alcohol condensates over 78 ºC 24. Say whether it is true or false: a. Each pure substance has got a melting and a boiling point. b. The melting point is the same as the solidification temperature.

25. Complete the following sentences with the appropiate words: a. Forces between gases molecules are……………….. b. The…..……………. of the particles is proporcional to its kinetic energy c. When the gas temperatura increases, it also increases its……… d. If the kinetic energy increases the particles collide more often and the………………..increases.

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