Question

For the combustion of n-octane
$C_8H_18 + O_2 \to CO_2 + H_2O$ at $25^{\circ}C$ (ignoring resonance in $CO_2$)

• A. $\Delta H= \Delta E-5.5 \times 8.31 \times 0.298\, in\, kJ/mol$
• B. $\Delta H = \Delta E+ 4.5 \times 8.31 \times 0.298\, in\, kJ/mol$
• C. $\Delta H = \Delta E - 4.5 \times 8.31 \times 0.298\, in\, kJ/mol$
• D. $\Delta H = \Delta E - 4.5 + 8.31 \times 0.298\, in\, kJ/mol$

Answer 1

Answer: (C)

$_{C_8H_{18}\left(l\right)}+12.5 O_{2_{\left(g\right)}}\to8CO_{2_{\left(g\right)}}+9H_{2}O_{\left(l\right)}$
$\Delta H=\Delta E+\left(8-12.5\right)\times8.31\times0.298$ in $kJ/mol$