One variety of household fuel is a mixture of propane (60%) and butane (40%). If 20 litres of this mixture is burnt, find the total volume of carbon dioxide added to the atmosphere. The combination reactions can be represented as:

C₃H₈ + 5O₂ ⟶ 3CO₂ + 4H₂O

2C₄H₁₀ + 13O₂ ⟶ 8CO₂ + 10H₂O

Given, 20 litres of this mixture contains 60% propane and 40% butane. Hence, propane is 12 litres and butane is 8 litres

$\begin{matrix} \text{C}$3\text{H}8 & + & 5\text{O}2 & \longrightarrow & 3\text{CO}2 & + & 4\text{H}2\text{O} \\ 1 \text{ vol.} & : & 5 \text{ vol.} & \longrightarrow & 3\text{ vol.} \\ 2\text{C}_4\text{H}_{10} & + & 13\text{O}2 & \longrightarrow & 8\text{CO}2 & + & 10\text{H}2\text{O} \\ 2 \text{ vol.} & : & 13 \text{ vol.} & \longrightarrow & 8\text{ vol.} \\ \end{matrix}

1 Vol. C₃H₈ produces carbon dioxide = 3 Vol

So, 12 litres C₃H₈ will produce carbon dioxide = 3 x 12 = 36 litres

2 Vol. C₄H₁₀ produces carbon dioxide = 8 Vol

So, 8 litres C₄H₁₀ will produce carbon dioxide = $\dfrac{8}{2}$ x 8 = 32 litres

Hence, 68 (i.e., 36 + 32) litres of CO₂ is produced.