STOICHIOMETRY Calculations Based on Chemical Equations

Iron (III) oxide reacts with carbon monoxide to form iron and carbon dioxide. Fe 2 O 3 +CO  Fe+CO How many CO molecules are required to react with 25 particles of Fe 2 O 3 ?

Iron (III) Oxide reacts with carbon monoxide to form iron and carbon dioxide. Fe 2 O 3 +CO  Fe+CO How many iron atoms can be produced by the reaction of 2.5 x 10 5 particles of Fe 2 O 3 ?

STOICHIOMETRIC RELATIONSHIPS Formulas can also represent MOLES of substances involved in chemical reactions. Equations define reaction ratios, i.e. the molar ratios of reactants and products

What mass of CO is required to react with 146 grams of iron (III) oxide? Fe 2 O 3 +3CO  2Fe+3CO 2

What mass of iron (III) oxide is required to produce 8.65 grams of carbon dioxide? Fe 2 O 3 +3CO  2Fe+3CO 2

Limiting Reactants (Reagents) and Percent Yield

Calculations need to be based on the limiting reactant. Example 1: Suppose a box contains 87 bolts, 110 washers and 99 nails. How many sets of 1 bolt, 2 washers and 1 nail can you use to create? What is the limiting factor? 55 sets; washers limit the amount

Calculations need to be based on the limiting reactant. Example 2: What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen? CS 2 + O 2  CO 2 + SO 2 Start by balancing the equation…

Calculations need to be based on the limiting reactant. Example 2: What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen? CS 2 + 3O 2  CO 2 + 2SO 2 Now solve the problem…

Example 2: What is the maximum mass of sulfur dioxide that can be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen? CS 2 + 3O 2  CO 2 + 2SO 2 Which reactant is LIMITING?

Example 2: What is the mass of sulfur dioxide that can be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen? CS 2 + 3O 2  CO 2 + 2SO 2 O 2 limits the amount of SO 2 that can be produced. CS 2 is in excess.

Example 2: What is the mass of sulfur dioxide that can be produced by the reaction of 95.6 g carbon disulfide with 100. g oxygen? CS 2 + 3O 2  CO 2 + 2SO g of SO 2 can be produced in this reaction.

Calculations need to be based on the limiting reactant. Example 3: What mass of CO 2 could be formed by the reaction of 8.0 g CH 4 with 48 g O 2 ? CH 4 + O 2  CO 2 + H 2 O Start by balancing the equation…

Calculations need to be based on the limiting reactant. Example 3: What mass of CO 2 could be formed by the reaction of 8.0 g CH 4 with 48 g O 2 ? CH 4 + 2O 2  CO 2 + 2H 2 O Now solve the problem…

Example 3: What mass of CO 2 could be formed by the reaction of 8.0 g CH 4 with 48 g O 2 ? CH 4 + 2O 2  CO 2 + 2H 2 O Which reactant is LIMITING?

Example 3: What mass of CO 2 could be formed by the reaction of 8.0 g CH 4 with 48 g O 2 ? CH 4 + 2O 2  CO 2 + 2H 2 O CH 4 limits the amount of CO 2 that can be produced. O 2 is in excess.

Many chemical reactions do not go to completion (reactants are not completely converted to products). Percent Yield: indicates what percentage of a desired product is obtained.

So far, the masses we have calculated from chemical equations were based on the assumption that each reaction occurred 100%. The THEORETICAL YIELD is the yield calculated from the balance equation. The ACTUAL YIELD is the amount “actually” obtained in an experiment.

Look back at Example 2. We found that 134 g of SO 2 could be formed from the reactants. In an experiment, you formed 130 g of SO 2. What is your percent yield?

Example: A 10.0 g sample of ethanol, C 2 H 5 OH, was boiled with excess acetic acid, CH 3 COOH, to produce 14.8 g of ethyl acetate, CH 3 COOC 2 H 5. What percent yield of ethyl acetate is this? CH 3 COOH + C 2 H 5 OH  CH 3 COOC 2 H 5 + H 2 O

Example: A 10.0 g sample of ethanol, C 2 H 5 OH, was boiled with excess acetic acid, CH 3 COOH, to produce 14.8 g of ethyl acetate, CH 3 COOC 2 H 5. What percent yield of ethyl acetate is this?