Consider the following equation for the combustion of acetone (C3H6O), the main ingredient in nail polish remover.

C3H6O (l) + 4O2 (g) →3CO2 (g) + 3H2O (g)

ΔHrxn=-1790kJ

a) If a bottle of nail polish remover contains 158 g of acetone, how much heat would be released by its complete combustion?

Octane (C8H18) is a component of gasoline that burns according to the following equation:

C8H18 (l) + 252O2 (g) →8CO2 (g) + 9H2O (g)

ΔH∘rxn=-5074.1kJ

a) What mass of octane (in g) is required to produce 1950 kJ of heat?

a) 4869 kJ will be released

b) 43.86 g of octane

Explanation:

The heat of combustion is the amount of heat released when 1 mol of a substance reacts with enough oxygen.

Since the heat of combustion is per mol of combustible substance what we are required to do in this problem is calculate number moles in the reactions although in a different manner.

a) MW C3H6O = 158 g/mol

mol C3H6O = 158 g x 1 mol/58.08 g = 2.72

-1790 kJ / mol x 2.72 mol = 4869 kJ

b) Here we are asked the mass of octane to produce 1950 kJ of heat knowing that per mol of octane we get 5074.1 kJ, then

1 mol / 5074.1 kJ x 1950 kJ = 0.384 mol

mass C8H18 = 0.384 mol x 114.23 g/mol = 43.86 g