Stoichiometry – Chapter 12

Stoichiometry – Chapter 12

Stoichiometry

• We are going to use the ‘mole’ to convert from one substance to another substance.

• You need to look at a balanced chemical reaction in order to determine the molar ratio between 2 substances.

Stoichiometry

• 4HNO3 (aq) + Sn (s) SnO2 (s) + 4NO2 (g) + 2H2O (l)

• You need to look at a balanced chemical reaction in order to determine the molar ratio between 2 substances.

Stoichiometry

• 4HNO3 (aq) + Sn (s) SnO2 (s) + 4NO2 (g) + 2H2O (l)

• Molar ratios: 4 mole HNO3 4 mole HNO3

1 mole Sn 1 mole SnO2

4 mole NO3 4 mole NO3 1 mole Sn 1 mole Sn

4 mole NO2 2 mole H2O 1 mole SnO2 4 mole NO2

1 mole Sn 1 mole SnO2 1 mole SnO2 * You can also use the

2 mole H2O 4 mole NO2 2 mole H2O the inverse of these. *

Stoichiometry• Write all of the molar ratio’s from the following

chemical reaction;C25H52(g) + 38O2(g) 25CO2(g) + 26H2O(g)

Stoichiometry

• 4HNO3 (aq) + Sn (s) SnO2 (s) + 4NO2 (g) + 2H2O (l)

• Calculate the mass of water produced if 10.00 grams of nitric acid is allowed to react.

• Calculate the mass of nitrogen dioxide produced if 10.00 grams of nitric acid reacted.

Stoichiometry

• Limiting Reactants• Eventually, one of the reactants will be used up first.

This reactant is called the limiting reactant.

• To determine which reactant is limiting, calculate the theoretical amount of product you should produce. The reactant that produces the least amount of reactant is the limiting reactant.

Stoichiometry

• Limiting ReactantsH2O (l) + CO2 (g) H2CO3 (aq)

If 5.00 grams of H2O is allowed to react with 2.50 grams of CO2, what is the maximum amount of H2CO3 that could be produced?

Which is the limiting reactant?

Stoichiometry• Limiting Reactants

CaCl2 (aq) + Na2CO3 (aq) 2NaCl (aq) + CaCO3 (s)

• What mass of NaCl would be produced if 1.0 kg of each reactant is used to produce sodium chloride and calcium carbonate?

• Which is the limiting reactant?

• Calculate the mass of the non-limiting reactant.

Stoichiometry• Reagents in Excess• A reactant that is not used-up completely in a chemical reaction

is called the reagent in excess.

4Na (s) + O2 (g) 2Na2O (s)

• What mass would remain of the reagent in excess if 0.60 moles of Na is placed in a reaction vessel that contains 1.0 L of O2 at STP?

Stoichiometry• Calculating Percent Yield• There are many factors that affect the yield of a

product in a chemical reaction. Pressure, temperature, volume, catalysts, and closed systems all affect the amount of product that is produced in a chemical reaction.

• The Percent Yield of a chemical reaction is the amount of product that was recovered as a percentage of the theoretical amount that should have been produced.

Stoichiometry• Calculating Percent Yield• The Theoretical Yield of a chemical reaction

is the amount of product that should be produced given that all of the limiting reactant will allow

% Yield = Amount Recovered x 100 Theoretical Yield

Stoichiometry• Calculating Percent Yield

4Na (s) + O2 (g) 2Na2O (s)

• Calculate the theoretical yield of Na2O if 5.00 grams of Na is added to 7.50 grams of O2.

Stoichiometry• Calculating Percent Yield

4Na (s) + O2 (g) 2Na2O (s)

• Calculate the percent yield of the reaction if 6.00 grams of Na2O was recovered.

Stoichiometry• Calculating Percent Yield

Ca(NO3)2 (aq) + NaCO3 (aq) 2NaNO3 (aq) + CaCO3 (s)

2.00 g of Ca(NO3)2 is added to 3.00 g of NaCO3. 0.750 g of the precipitate was isolated from the chemical reaction. What is the percent yield of this chemical reaction?