(a)
C (graphite)+$\frac{1}{2}O_{2}(g) \rightarrow CO(g)$
$\mathrm{\Delta}n_{g} = 1 - \frac{1}{2} = \frac{1}{2}$
$\mathrm{\Delta}H = \mathrm{\Delta}E + \mathrm{\Delta}n_{g}RT$
$\mathrm{\Delta}E = \mathrm{\Delta}E - \mathrm{\Delta}n_{g}RT$
$= - 26.4 - \frac{1}{2} \times 0.002 \times 298$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = - 26.7$ kcal