Stoichiometry for Dummies
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Increase your test scores Practice with a short length quiz and a puzzle Everything you need to pass the stoichiometry part of the New York State Regents Feeling of confidence
Brooklyn Technical High School Mr.Asher, Principal Mr.Evangelist, A.P. Supervision of Science Mr.Nair, Instructor Jonathan Cheng, Student
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Stoichiometry for Dummies
BTHS Chemistry
BTHS Chemistry
Stoichiometry for Dummies
Stoichiometry for Dummies Table of Contents
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Chapter 1........................................................................................................4 Chapter 2........................................................................................................7 Chapter 3......................................................................................................10 Chapter 4......................................................................................................13
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Stoichiometry for Dummies
Chapter 1: Formulas/Equations
Before we start off into formulas and equations, what are formulas and equations? formula - A set of chemical symbols showing the elements present in a compound and their relative proportions. equation - a statement that the values of two mathematical expressions are equal element - A substance that cannot be decomposed into simpler substances by chemical means Now that you know the definitions of those two words, what is a chemical reaction? chemical reaction - a process where one or more starting substances change into one or more final substances Before we write a chemical reaction, what are the parts of a chemical reaction? A chemical reaction consists of two parts: coefficients - gives ratio of reactants and products in a balanced chemical equation reactants - left side of reaction arrow products - right side of reaction How do we write chemical equations? There are two typed of chemical equations that we can write. They are the following: word equation - a statement that involves the written name of the chemical compund to describe the reaction Ex. copper + sulfur → copper sulfide formula equation - a statement that involves the chemical formulas of the chemical compound to describe the reaction Ex. Cu + S → CuS More Examples of Word and Formula Equations Word Equation Ethane + Oxygen → Carbon dioxide + Water Aluminium + Hydrochloric acid → Aluminium chloride + Hydrogen Formula Equation C + O2 → CO2 N2 + 3H2 → 2NH3
Stoichiometry for Dummies
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Understand everything so far? Aright. Now how do we actually solve these problems? Word to Formula Formula to Word 1. Find the names of the elements or 1. Find the chemical symbol in a recompunds in a refrence tabele. frence table. 2. Write them out in the same order as 2. Write them out in the same oder as the word formula. the formula equation. Test Yourself 1. Convert the following to a word equation: Zn + AgNO3 → Ag + Zn(NO3)2 Answer: zinc + silver nitrate → silver + zinc nitrate Why? Zn = zinc AgNO3 = silver nitrate Ag = silver Zn(No3)2 = nitrate 2. Convert the following to a formula equation: Sodium chloride is produced when sodium metal reacts with chlorine Answer: Na + Cl → NaCl Why? sodium = Na chlorine = Cl NaCl = Sodium chloride Great job making it this far! There are many types of reactions but before we learn them, there are two therms that we must know. They are: endothermic reaction - a reaction which absorbs heat from the surroundings Ex. Melting of ice (solid to liquid Evaporation of water (liquid to gas) exothermic reaction - a reaction which releases heat Ex. Wood burning Turning on a lamp Types of Reactions There many types of reaction and chemicals react in many different ways. The 5 types of reactions are: synthesis reaction - a reaction where one element replaces another element in a compound Ex. A + B → AB or 8 Fe + S8 → 8 FeS decomposition reaction -a reaction where two compounds trade their elements (or polyatomic ions) Ex. AB → A + B or 2 H2O → 2 H2 + O2 single replacement reaction - a reaction where two or more reactants combine to form only 1 product Ex. A + BC → AC + B or Zn + 2 HCl → ZnCl2 + H2
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Stoichiometry for Dummies
double replacement reaction - a reaction where 1 reactant breaks down to form two or more products (opposite of a synthesis reaction) Ex. A+B- + C+D- → A+D- + C+B- or AgNO3 + NaCl → AgCl + NaNO3 combustion reaction - a reaction where a substance burns in the presence of oxygen Ex. C10H8 + 12 O2 → 10 CO2 + 4 H2O Conclusion Great job for making it through the first chapter! Now for some review. What have we gone over so far? Definitions • formula • equation • chemical reaction • coefficients • reactants • products • word equations • endothermic reaction • exothermic reaction • synthesis reaction • decompotion reacation • single replacement reaction • double replacement reaction • combustion reaction Skills • convert word equations to formula equations. • convert formula equations to word equations.
Stoichiometry for Dummies
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Chapter 2: Math in Chemistry
Welcome to Chapter 2 of Stoichiometry for Dummies! In this chapter we will be doing math just like what the title says. First off, what is a mole? An animal? NO. mole - a number that can represent anything numerically Ex. 10 mole of cheese 1 mole of crackers Only one mole of crackers for 10 moles of cheese? You may not think that is much but what does a mole equal to? Mole Identities • 1 mole = 6.02 x 1023 molecules • 1 mole = 22.4 Liters of a gas at STP • 1 mole = GFM molecules - a group of atoms bonded together STP - standard temperature and pressure (Pressure - 101.3 kPa(kilopascal) or 1 atm(atmosphere)) (Temperature - 273 K(kelvin) or 0oC(degree Celsius))
We are nearing the math part in chemistry but first we need to know what percomposition. Uh-oh it says percents. Percents? Easy. percent composition - the mass percent of each element in a compound % composition by mass = mass of part/mass of whole x 100 How to Calculate Percent Composition Lets find the percent composition of H in H2O 1. Add up all the atoms of one element and find its total mass. In this case, we are finding the percent composition of H’s so we add up the mass of all the H’s. 1 H = 1.00794 grams so 2H’s = 2.01588 grams. H2 = 2.01588 grams 2. Find the total mass of the compund by adding up all the masses. O = 15.9994 grams so the total mass of the compund is 15.9994+2.01588 grams 3. Divide the mass of the part (step1) by mass of the whole (step 2). 2.01588/18.01528 = approximately 0.11189 4. Multiply by 100. 0.1189 x 100 = approzimately 11.19% Answer: approximately 11.19%
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Stoichiometry for Dummies
Gram atomic mass and gram formula mass. What? Aren’t they the same? gram atomic mass - mass of an atom in grams Ex. What is the gram atomic mass of oxygen? 1. Find oxygen in your reference table. the gram atomic mass should be in the top. Answer: 15.9994 grams gram formula mass - mass of a compound in grams Ex. What is the gram formula mass of silver nitrate (AgNO3)? 1. Find Ag in your reference table and determine the mass. Do this for all the elements. Ag - 107.868 N - 14.0067 O - 15.9994 2. Multiply each element by how many there are. 1 Ag = 107.868 x 1 = 107.868 1 N = 14.0067 x 1 = 14.0067 3 O = 15.9994 x 3 = 47.9982 3. Now add it all up! 107.868 14.0067 47.9982 Answer: 169.8729 grams Did you follow along? If not, look that section over. It’s just finding numbers and doing simple math. Now lets put what we learned right now together. And why would we want to that? To work more with moles because we love the so much! molar mass - the mass of one mole of a substance (units in grams/mole) So how is atomic mass and gram formula mass connected to molar mass? Essentially, they are almost the same thing. They are the mass of something but just parts. Many gran atomic masses together can be become a gram formula mass. Molar mass is almost like gram formula mass but with the mole component in the units (grams/mole). Test Yourself Determine the gram formula mass for O2, H2, H2O, and NH3. O = 15.9994 H = 1.00794 N = 14.0067 O = 15.9994 x 2 = 31.9988g H = 1.00794 x 2 = 2.01588g H = 1.00794 x 2 = 2.01588 H2 = 2.01588g O = 15.9994 x 2 = 31.9988 O2 = 31.9988g N = 14.0067 x 1 = 14.0067 H20 = 34.01468g H = 1.00794 x 3 = 3.02382 14.0067 + 3.02382 = 17.03052g = NH3
Stoichiometry for Dummies
Conclusion
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What have we learned in this chapter? Many important things! But do you remember what they are? Definitions • mole • percent composition • gram atomic mass • gram formula mass • molar mass Skills • calculate percent composition • calculate gram atomic mass • calculate gram formula mass
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Stoichiometry for Dummies
Chapter 3: Balancing Equations
This is the chapter before the review! Congratulations for making this far. Now that we have a very good understanding of the basic things, it is time for the more challenging part: learning how to balance equations. But before learning how to balance equations, we must learn a few definitions. subscript - number indicating how many of a certain element are present in a compound; written below the line coefficient - the number preceding an element or compound in a chemical equation; they are multipliers
The Law of Conservation of Matter Every single atom which goes into a chemical reaction must come out the other side. Matter is neither created nor destroyed.
2 Yellow 3 Red 5 Blue
2 Yellow 3 Red 5 Blue
Diatomic Molecules
Certain nonmetals exist in nature as diatomic molecules or in other words they exist as two atoms bonded together. These elements are hydrogen, oxygen, fluorine, bromine, iodine, nitrogen, and chlorine Therefore, when we mention these elements, we must know they exist as H2, O2, F2, Br2, I2, N2, andCl2
Stoichiometry for Dummies
atom - the smallest particle of an element Ex. hydrogen helium molecule - a complete chemical unit Ex. Br2 - 1 molecule 2Ag - 2 molecules Test Yourself How many molecules are in each? Atoms? O2, H2, H2O, 2O2, 3H2, 4H2O 1. O2 1 molecules 2 atoms 2. H2 1 molecule 2 atoms 1 molecule 3 atoms 3. H2O 4. 2O2 2 molecules 4 atoms 5. 3H2 3 molecules 6 atoms 6. 4H2O 4 molecules 12 atoms
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balanced equation - an equation for a chemical reaction in which the mass and the charge are balanced on both sides of the reaction. Knowing what a balanced equation is, we can start to balance equations out. Subscripts CANNOT be changed. They are two powerful despite their small size so we only change coefficients. 1. Pick one type of molecule in the equation and balance it on both sides making sure that both sides have the equal ammount of atoms. 2. Continue to pick the next molecule and balance it out. Repeat untill all coefficients places have been filled. 3. Lastly, check work by counting the amount of atoms Test Yourself Balance the following equations. 1. C3H8(g) + O2(g) → H2O(g) + CO2(g) 1C3H8(g) + _O2(g) → _H2O(g) + 3CO2(g) The left side has 3 C’s so lets make the right side have 3 C’s. 1C3H8(g) + _O2(g) → 4H2O(g) + 3CO2(g) The left side has 8 H’s so lets make the right side have 8 H’s. 1C3H8(g) + 5O2(g) → 4H2O(g) + 3CO2(g) The left side has10 O’s so lets make the right side have 10 O’s. Check! Both sides have 3 C’s, 8 H’s, and 10 O’s.
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Stoichiometry for Dummies
2. CH4(g) + O2(g) → CO2(g) + H2O + energy 1CH4(g) + _O2(g) → _CO2(g) + 2H2O + energy The left side has 4 H’s so lets make the right side have 4 H’s. 1CH4(g) + _O2(g) → 1CO2(g) + 2H2O + energy The left side has 1 C’s so lets make the right side have 1 C’s. 1CH4(g) + 1O2(g) → 1CO2(g) + 2H2O + energy The left side has 2 O’s so lets make the right side have 2 O’s. Check! Both sides have 1 C’s, 4 H’s, and 2 O’s. 3. AgNO3 + MgCl2 → Mg(NO3)2 + AgCl 2AgNO3 + _MgCl2 → 1Mg(NO3)2 + _AgCl The right side has 6 O’s so lets make the left side have 6 O’s. 2AgNO3 + _MgCl2 → 1Mg(NO3)2 + 2AgCl The left side has 2 Ag’s so lets make the right side have 2 Ag’s. 2AgNO3 + 1MgCl2 → 1Mg(NO3)2 + 2AgCl The right side has 2 Cl’s so lets make the left side have 2 Cl’s. Check! Both sides have 6 O’s, 2 Ag’s, and 2 Cl’s. Conclusion Wow that was intense? Did you get everything? Hope you did so hear is what we learned in the third chapter.
Definitions • subscript • coefficient • balanced equation • Law of Conservation of Matter Skills • Determine number of molecules in a compound. • Determine number of atoms in a compound. • How to balance an equation
Stoichiometry for Dummies
Chapter 4: Review
Matching Match each word to its definition. 1. word equation _____ 2. synthesis reaction _____ 3. mole _____ 4. gram formula mass _____ 5. balanced equation _____
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a. a reaction where one element replaces another element in a compound b. a number that can represent anything numerically c. a statement that involves the written name of the chemical compund to describe the reactionl d. mass of an atom in grams e. an equation for a chemical reaction in which the mass and the charge are balanced on both sides of the reaction.
True or False If it is false then change the statement so that it is true. 1. T / F Subscripts can be changed. 2. T / F Matter can be created 3. T / F A coefficient is the a number preceding an element or compound 4. T / F 1 mole = 6.02 x 1023 molecules 5. T / F There are 12 atoms in 4H2O Word Search