Question

LPG stands for liquefied petroleum gas. Varieties of LPG are marketed including a mixture of propane (60%) and butane (40%). If 10 litres of this mixture is burnt, find the total volume of carbon dioxide gas added to the atmosphere. Combustion reaction can be represented as:

\[\ce{C3H8_{(g)} + 5O2_{(g)} -> 3CO2_{(g)} + 4H2O_{(g)}}\]

\[\ce{2C4H10_{(g)} + 13O2_{(g)} -> 8CO2_{(g)} + 10H2O_{(g)}}\]

Answer 1

% of propane = 60%

% of butane = 40%

Total volume of the mixture = 10 litres

Propane = `60/100 xx 10` = 6 litres

Butane = `40/100 xx 10` = 4 litres

(i) Combustion of propane:

C3H8(g)	+	5O2(g)	→	3CO2(g)	+	4H2O(g)
1 vol.						3 vol.
6 litres						?

1 vol of propane releases 3 vol of CO₂

6 litres of propane releases `3/1 xx 6` litres = 18 litres

(ii) Combustion of butane:

2C4H10(g)	+	13O2(g)	→	8CO2(g)	+	10H2O(g)
2 vol.				8 vol.
1 vol.				4 vol.
4 litres				?

2 vol of butane releases 8 vol of CO₂

4 litres of butane releases `8/2 xx 4` = 16 litres

Total CO₂ released O₂ = 18 L + 16 L

= 34 litres of CO₂ gas is added to the atmosphere.