Stoichiometry Chemistry II Chapter 9

Reaction Stoichiometry Based on conservation of matter Balanced equation If the quantity of one substance is known, others can be found Mole ratios

5 Step Process Construct a balanced equation. Identify known(s) and unknown(s). Convert known(s) to moles (if necessary). Find moles of unknown(s). Convert unknown(s) into required units (if necessary).

Example Problem How many grams of nitrogen will react with 112 L of hydrogen to form ammonia (NH3)?

Step One: Construct a Balanced Chemical Equation Nitrogen and hydrogen produce ammonia N2 + H2  NH3 Be honest, did you forget the 2’s? N2 + 3H2  2NH3

Step Two: Identify Known(s) and Unknown(s) N2 + 3H2  2NH3 ?g 112 L

Step Three: Convert Known to Moles 112L H2 * 1 mol H2 = ? mol H2 22.4 L H2

Step Three: Convert Known(s) to Moles 112L H2 * 1 mol H2 = 22.4 L H2 5 mol H2

Step Four: Find Moles of Unknown(s) Convert moles of known to moles of unknown. Use the mole ratio from the balanced equation.

Step Four: Find Moles of Unknown(s) N2 + 3H2  2NH3 5 mol H2 * 1 mol N2 = ? Mol N2 3 mol H2

Step Four: Find Moles of Unknown(s) N2 + 3H2  2NH3 5 mol H2 * 1 mol N2 = 1.67 Mol N2 3 mol H2

Step Five: Convert Unknown(s) into Required Units How many grams of nitrogen? 1.67 Mol N2 * 28 g N2 = ? g N2 1 mol N2

Step Five: Convert Unknown(s) into Required Units How many grams of nitrogen? 1.67 Mol N2 * 28 g N2 = 1 mol N2 46.76 g N2

Your Turn…. 560 L of oxygen will react with hydrogen to make how many grams of water?

One: Construct a Balanced Chemical Equation Oxygen and hydrogen produce water O2 + H2  H2O O2 + 2H2  2H2O

Two: Identify Known(s) and Unknown(s) O2 + 2H2  2H2O 560 L ?g

Three: Convert Known(s) to Moles 560 L O2 * 1 mol O2 = 25 mol O2 22.4 L O2

Four: Find Moles of Unknown(s) O2 + 2H2  2H2O 25 mol O2 * 2 mol H2O = 1 mol O2 50 Mol H2O

Five: Convert Unknown(s) into Required Units 50 Mol H2 O * 18 g H2 O = 900 g H2 O 1 mol H2O

The End??