Balanced Equations Show Proportions A balanced chemical equation is very similar to a recipe in that the coefficients in the balanced equation show the proportions of the reactants and products involved in the reaction. On a very small scale, the coefficients in a balanced equation represent the numbers of particles for each substance in the reaction. For example: 2H 2 + O 2 → 2H 2 O The balance equation above states that 2 hydrogen molecules are reacting with 1 oxygen molecule to produce 2 water molecules.

Relative Amounts in Equations Can Be Expressed in Moles Just as you can interpret equations in terms of particles, you can interpret them in terms of moles. The coefficients in a balanced equation also represent the moles of each substance. For example: 2H 2 + O 2 → 2H 2 O The balance equation above states that 2 moles of hydrogen molecules are reacting with 1 mole of oxygen molecule to produce 2 moles of water molecules.

The Mole Ratio The coefficients in a balanced chemical equation show the relative numbers of moles of the substances in the reaction. As a result, you can use the coefficients in conversion factors called mole ratios. Mole ratios bridge the gap and can convert from moles of one substance to moles of another. For example: 2H 2 + O 2 → 2H 2 O In the equation above the mole ration between oxygen and water is1:2 This means that for every mole of oxygen used 2 moles of water are produced It also means that for every mole of water produced only 0.5 moles of oxygen are used.

Practice Make Perfect 1. Given the balanced equation representing a reaction: F 2 (g) + H 2 (g)  2HF(g) What is the mole ratio of H 2 (g) to HF(g) in this reaction? 1:2 2. Given the reaction: PbCl 2 (aq) + Na 2 CrO 4 (aq)  PbCrO 4 (s) + 2NaCl(aq) What is the total number of moles of NaCl formed when 2 moles of Na 2 CrO 4 react completely? 4 moles of NaCl

3. Given the balanced equation: 2C 4 H 10 (g) + 13O 2 (g)  8CO 2 (g) + 10H 2 O(g) What is the total number of moles of O 2 (g) that must react completely with 5.00 moles of C 4 H 10 (g)? 4. Given the balanced equation: 2C + 3H 2  C 2 H 6 What is the total number of moles of C that must completely react to produce 2.0 moles of C 2 H 6 ? 5. Given the equation: 2C 2 H 2 (g) + 5O 2 (g)  4CO 2 (g) + 2H 2 O(g) How many moles of oxygen are required to react completely with 1.0 mole of C 2 H 2 ? 2.5 moles of O 2 4 moles of Carbon 32.5 moles of O 2

6. Given the reaction: N 2 (g) + 3H 2 (g)  2NH 3 (g) What is the mole-to-mole ratio between nitrogen gas and hydrogen gas? 7. Given the reaction: 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 What is the total number of moles of water needed to make 2.5 moles of C 6 H 12 O 6 ? 1:3 15 moles of water

Questions 8 and 9 refer to the following: Given the reaction: 2C 2 H 6 + 7O 2  4CO 2 + 6H 2 O 8) What is the ratio of moles of CO 2 produced to moles of C 2 H 6 consumed? 9) What is the total number of moles of CO 2 produced by the complete combustion of 5.0 moles of C 2 H 6 ? 10 moles of CO 2 4:2  2:1