Chapter 10 – Introduction to Equations Writing and Balancing Equations Section 10.1

C8H18 + O2 -> CO2 + H2O + ENERGY Chemical Reactions One or more substances are rearranged to form different substances C8H18 + O2 -> CO2 + H2O + ENERGY LOOK, IT’S A HYDROCARBON!!!!! The products are carbon dioxide and water!

Indicators of Chemical Reactions Animation of Experiment (GIF Format, 321 k) Temperature Change Color Change Odor Production of Gas Bubbles Production of a Precipitate

Representing Chemical Reactions Symbol Meaning + Separates two or more reactants or products -> Separates reactants from products (s) Solid state (l) Liquid state (g) Gaseous state (aq) Water solution Statements called equations are used to describe what happens during a chemical reaction Reactants are the starting substances found on the left side of the equation Products are the substances formed during a reaction

Word Equations and Skeleton Equations -Statements that indicate the reactants and products in a rxn -Describe chemical reactions -Lack important information Iron (s) + chlorine (g) -> iron (III) chloride (s) Skeleton Equations -Uses chemical formulas to identify reactants and products Fe (s) + Cl2 (g) -> FeCl3 (s)

Practice Problems Write skeleton equations for the following word equations: 1. hydrogen (g) + bromine (g) -> hydrogen bromide (g) H2 (g) + Br2 (g) -> HBr (g) 2. carbon monoxide (g) + oxygen (g) -> carbon dioxide (g) CO (g) + O2 (g) -> CO2 (g) 3. potassium chlorate(s) -> potassium chloride(s) + oxygen(g) KClO3 (l) -> KCl (s) + O2 (g)

A Balanced Chemical Equation Balancing Equations Chemical Equations also must obey the Law of Conservation of Mass. The number of atoms that are used in the reactants must equal the number of atoms found in the products. Matter can neither be created nor destroyed. A chemical equation that follows the law of conservation of mass is called a balanced chemical equation. A Chemical Equation H2 + O2 -> H20 A Balanced Chemical Equation Coefficient… -> 2H2 + O2 -> 2H2O

Balancing Chemical Equations There is a procedure for balancing chemical equations: Write the equation (remember your diatomic molecules) Count the atoms of each element Add or adjust the coefficients (subscripts cannot be changed) Reduce coefficients to lowest possible terms Check your work Hydrogen + Chlorine Yields Hydrochloric Acid H2 + Cl2 -> HCl

Balancing Equations Practice Al + O2 -> Al2O 4Al + O2 -> 2Al2O C3H8 + O2 -> CO2 + H2O C3H8 + 5O2 -> 3CO2 + 4H2O KNO3 -> KNO2 + O2 2KNO3 -> 2KNO2 + 2O2 O2 + CS2 -> CO2 + SO2 3O2 + CS2 -> CO2 + 2SO2