“Chemical Reactions”
Notebox
Describing Chemical Reactions • OBJECTIVES: – Describe how to write a word equation. – Describe how to write a chemical equation.
Chemical Reactions Express how atoms combine or split apart to form new substances.
Examples – H 2 + O 2 H 2O CH4 + O2 CO2 + H2O
All chemical reactions… •
have two parts: 1. Reactants = the substances you start with 2. Products = the substances you end up with • The reactants will turn into the products. • Reactants → Products
If it were math… •
have two parts: 1. Reactants = Question (2+2) 2. Products = Answer (4) • The reactants will turn into the products. • Reactants → Products
In a chemical reaction • A reaction can be described several ways: 1) A word equation is a way of describing a chemical reaction using the names of the reactants and products e.g. Iron + sulfur iron (II) sulfide + energy
2) A chemical equation is a of way describing a chemical reaction using the chemical formula of the reactants and products e.g. Fe + S FeS
Symbols in equations? • the arrow (→) separates the reactants from the products (arrow points to products) – Read as: “reacts to form” or yields • The plus sign (+) = “and” meaning that they are in contact with each other
Symbols Con’t Only used in CHEMICAL EQUATIONS Includes a description of the state of the reactants and products • (s) after the formula = solid:
Fe(s)
• (g) after the formula = gas:
CO2(g)
• (l) after the formula = liquid:
H2O(l)
• (aq) after the formula = dissolved in water, an aqueous solution: NaCl(aq) is a salt water solution
e.g. Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s)
Energy • Energy can either be absorbed or released and is only written in a chemical equation • If it is absorbed it is written on the reactant side e.g. Energy + Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s)
• If it is released it is written on the product side. e.g. CuCO3(s) CO2(g) + CuO(s) + Energy
Energy • If Energy is absorbed it is taken from the environment feels cold (heat is energy)
• If Energy is released it is sent into the environment feels warm (heat is released)
Write a chemical equation for: 1. Solid iron (III) sulfide reacts with gaseous hydrogen monochloride to form iron (III) chloride, dihydrogen sulfide gas and energy. Fe2S3(s)+HCl(g) ďƒ FeCl3(g) + H2S(g) + Energy
Using energy, sodium chloride dissolves in water to form aqueous Sodium and Chloride Ions. Energy + NaCl(aq) ďƒ Na+ Cl-
Write a sentence for the following then write it as a word equation: Energy + Fe(s) + O2(g) → Fe2O3(s) Energy is used to react Solid Iron with oxygen gas to form Iron (III) Oxide Solid.
**states are not included in word equations**
What is a catalyst?
• A substance that speeds up a reaction, without being changed or used up by the reaction. • Enzymes are biological or protein catalysts in your body.