Question

The equation for the combustion of butane, C4H10, is:

2C4H10 (g)+13O2 (g)→8CO2 (g)+10H2O(g)

Which one of the following situations generates the smallest amount of heat? Motivate your answer.

a) Burning one mole of butane.

b) Reacting one mole of oxygen with excess butane.

c) Producing one mole of carbon dioxide by burning butane.

d) Producing one mole of water by burning butane.

Answer 1

The more butane is burnt, the more heat is produced. So calculating what quantites of butane undergo reaction in each case will show what amounts of heat are produced.

1) n(C₄H₁₀) = 1 mol

2) n(C₄H₁₀) = ${\frac {2} {13}}$ mol accroding to equation, as n(O₂) = 1 mol and n(C₄H₁₀) = ${\frac {2} {13}}$*n(O₂)

3) n(C₄H₁₀) = ${\frac {1} {4}}$ mol according to equation, as n(CO₂ produced) = 1 mol and n(C₄H₁₀) = ${\frac {2} {8}}$*n(CO₂)

4) n(C₄H₁₀) = ${\frac {1} {5}}$ mol according to equation, as n(H₂O produced) = 1 mol and n(C₄H₁₀) = ${\frac {2} {10}}$*n(H₂O)

the least amount of butane involved is in the second case, so the least amount of heat generated in 2 situation