1. Significance of Chemical Equations

2. What information? Coefficients indicate relative amounts of substances
May indicate molecules
May indicate moles
May indicate volumes of gases
Masses can be determined
Reverse reaction has same relative amounts of product and reactant

3. Balancing
Equation must have the same number of atoms (of each element) on both product and reactant side
Coefficients used to balance equation

4. Sample Problem 8-3
The reaction of zinc with aqueous hydrochloric acid produces a solution of zinc chloride and hydrogen gas. Write a balanced equation for this reaction.
Zn(s) + HCl(aq) → ZnCl2(aq) + H2(g)‏
Balance the equation!
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)‏

5. Sample Problem 8-4
Solid aluminum carbide (Al4C3) reacts with water to produce methane gas and solid aluminum hydroxide. Write a balanced chemical equation for this reaction.
Al4C3(s) + H2O(l) → CH4(g) + Al(OH)3(s)‏
Al4C3(s) + 12H2O(l) → 3CH4(g) + 4Al(OH)3(s)‏

6. Sample Problem 8-5
Aluminum sulfate and calcium hydroxide are added to water and dissolve and react to produce insoluble aluminum hydroxide and calcium sulfate. Write a balanced chemical equation for this reaction.
Al2(SO4)3(aq) + Ca(OH)2(aq) → Al(OH)3(s) + CaSO4(s)‏
Balance!
Al2(SO4)3(aq) + 3Ca(OH)2(aq) → 2Al(OH)3(s) + 3CaSO4(s)‏