Stoichiometry Predicting amounts of reagents needed or amounts of products made

2 C 2 H O 2  4 CO H 2 O How much CO 2 will be produced if 4 moles of C 2 H 6 are consumed? Identify a stoichiometry problem: 1) You always get a balanced chemical equation. 2) The problem will ask how many moles or how many liters given a certain amount of something else. 3) The equation has a  arrow.

2 C 2 H 6 4 CO 2 2 C 2 H O 2  4 CO H 2 O CO 2 C 2 H 6How much CO 2 will be produced if 4 moles of C 2 H 6 are consumed? 4X ___________ 4 moles C 2 H 6 2 moles C 2 H 6 = X moles CO 2 4 moles CO 2 X = 8 moles CO 2

2 C 2 H 6 6 H 2 O 2 C 2 H O 2  4 CO H 2 O H 2 O C 2 H 6How much H 2 O will be produced in the combustion of 5 moles of C 2 H 6 ? 5 X 5 moles C 2 H 6 ____________ 2 moles C 2 H 6 = X moles H 2 O ___________ 6 moles H 2 O X = 15 moles H 2 O

2 C 2 H 6 7 O 2 2 C 2 H O 2  4 CO H 2 O oxygen C 2 H 6How much oxygen will react with 5 moles of C 2 H 6 ? 5X 5 moles C 2 H 6 ___________ 2 moles C 2 H 6 = X moles O 2 ___________ 7 moles O 2 X = 17.5 moles O 2

Coefficients in Balanced Equations Give relative number of particles in rxn. Give relative number of moles in rxn. Coefficients give relationship between moles of each component in equation. You use these relationships in MOLE-MOLE problems to convert from moles of 1 substance to moles of another substance.

Gas-Phase Equations 1 mole of any gas occupies the same volume as any other gas. At STP, 22.4 L. So coefficients in equations represent the ratio of the volumes of gases involved in the reaction. For rxns where all reactants & products are gases,  volume-volume problems. Unit doesn’t matter as long as it’s constant throughout.

N 2 (g) + 3 H 2 (g)  2 NH 3 (g) How much hydrogen gas will react with 15 liters of nitrogen gas? 15 L N 2 (g) _________ 1 L N 2 (g) = X L H 2 (g) _________ 3 L H 2 (g) X = 45 L H 2 (g)

Limiting Reactant The limiting reactant –the reactant that is used up first –limits the amount of product that can be produced –there is usually only one limiting reactant By contrast, the reactant that is not completely used up is called the excess reactant.

Percent Yield The percent yield is the ratio of the actual yield to the theoretical yield, multiplied by 100 %. percent yield = actual yield x 100% theoretical yield The percent yield is a measure of the of a reaction.