Question

The difference between $\Delta$H and $\Delta$E (on a molar basis) for the combustion of n-octane ($\mathcal{l}$) at 25⁰C would be :

• A. – 13.6 kJ
• B. – 1.14 kJ
• C. – 11.15 kJ
• D.
  • 11.15 kJ

Answer 1

Answer: (C)

– 11.15 kJ

Answer 2

C8H18($\mathcal{l}$) + $\frac{25}{2}$O2 (g) $\longrightarrow$ 8CO2(g) + 9H2O ($\mathcal{l}$)

$\Delta$ng = 8 – $\frac{25}{2}$ = $\frac{16 - 25}{2}$ = – $\frac{9}{2}$ = – 4.5

$\Delta$H – $\Delta$E = $\Delta$ngRT = – $\frac{4.5 \times 8.314 \times 298}{1000}$ = –11.15 Kj