Section 11.3 – Stoichiometry of Gases

Stoichiometry The quantitative analysis of substances involved in chemical reactions.

Gay-Lussac and Avogadro We use their discoveries to calculate the coefficients in chemical reactions involving gases.

The Coefficients Represent The volume ratios of the gases involved, as well as the molar amounts and mole ratios. What are the possible volume ratios for this reaction?

Volume-Volume Calculations We assume that the volumes of both the reactants and products exist under the same temperature and pressure conditions.

Sample Problem #1 The complete combustion of propane: C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

What Will Be The Volume, In Liters, A. Of oxygen required for the complete combustion of 0.350 L of propane? B. Of carbon dioxide produced in the reaction?

Other Calculations Require The conditions under which the gas volumes were measured.

Volume-Mass Calculations gas volume A → moles A → moles B → mass B

Sample Problem #2 How many grams of calcium carbonate must be heated to produce 5.00L of carbon dioxide gas at STP? CaCO3(s) → CaO(s) + CO2(g)

Mass-Volume Calculations mass A → moles A → moles B → gas volume B

Sample Problem #3 How many liters of hydrogen gas at 35°C and 0.980 atm are needed to react completely with 875 g of tungsten oxide? WO3(s) + 3H2(g) → W(s) + 3H2O(l)