1. Reaction Stoichiometry

2. Objectives Understand the concept of stoichiometry. Be able to make mass-to-mass stoichiometric calculations.

3. Stoichiometry stoichiometry: the process of calculating quantities involved in chemical reactions balanced chemical equations are required coefficients can represent the number of particles or the number of moles N 2 (g) + 3H 2 (g) → 2NH 3 (g) 1 mole 3 moles 2 moles mole ratio: ratio of moles involved in a reaction (using coefficients)

4. Stoichiometry Problem N 2 (g) + 3H 2 (g) → 2NH 3 (g) If 25.7 g of nitrogen gas completely reacts with an excess of hydrogen gas, what mass of ammonia is produced? # g N 2 → # mol N 2 → # mol NH 3 → #g NH 3 g A → mol A → mol B → g B A B A = what you know B = what you want This “pathway” is used in most stoichiometry problems

5. Stoichiometry Problem The process of smelting iron ore to iron can be carried out with the following reaction. How much ferric oxide is needed to produce 75.8 g of iron using this method? Fe 2 O 3 (s) + 3 CO(g) → 2 Fe(s) + 3 CO 2 (g)

6. Stoichiometry Problem A copper penny combines with oxygen in a crucible to form cuprous oxide. Write a balanced chemical equation for the reaction. What mass of oxygen is needed to completely react with a 3.12 g copper penny?

7. Objectives Understand the distinction between actual yield and theoretical yield. Be able to determine the percentage yield for a chemical reaction.

8. Percentage Yield theoretical yield: the maximum amount of product that can be produced (calculated using stoichiometry) actual yield: the actual amount of product produced in a chemical reaction The percent yield cannot exceed 100%

9. Percentage Yield Problem What is the percentage yield if 4.65 g of copper is produced when 1.87 g of aluminum reacts with excess cupric sulfate? 2 Al (s) + 3 CuSO 4 (aq) → Al 2 (SO 4 ) 3 (aq) + 3 Cu (s)

10. Objective You will be able to determine the limiting reagent (or reactant) for a chemical reaction when given the mass of two (or more) reactants.

11. Limiting Reagent limiting reagent: the reactant that is completely consumed first in a reaction (so it limits the amount of product) The reactant that yields the least product is the limiting reagent. Which substance is the limiting reagent if 3.50 g of sulfur reacts with 2.50 g of aluminum to produce Al 2 S 3 ? How much Al 2 S 3 is actually produced?