Question

If $\Delta E$ is the heat of rection for
$C_2{H}_{5}OH\left(l\right)+3O_2\left(g\right)⟶2{CO}_2\left(g\right)+3H_{2}O\left(l\right)$
at constant volume, the $\Delta H$ (heat of reaction at constant pressure), at constant temperature is:

• A. $\Delta H=\Delta E+RT$
• B. $\Delta H=\Delta E-RT$
• C. $\Delta H=\Delta E-2RT$
• D. $\Delta H=\Delta E+2RT$

Answer 1

Answer: (B)

$\Delta H=\Delta E-RT$

We know that,

$\Delta H=\Delta E+\Delta nRT$

where

$\Delta n=$number of moles of gaseous products-number of moles of gaseous reactants$=2-3=-1$

So, $\Delta H=\Delta E-RT$