Which of the following symbols represent heat of reaction at constant volume?
Which of the following symbols represent heat of reaction at constant volume?
$\Delta \mathrm{H}$
dq
$\Delta \mathrm{S}$
$\Delta \mathrm{U}$
Solution
According to the first law of thermodynamics, $\Delta \mathrm{U}=\mathrm{Q}+\mathrm{W}=\mathrm{Q}-\mathrm{P}_{\text {ext }} \cdot \Delta \mathrm{V}\left(\because \mathrm{W}=-\mathrm{P}_{\text {ext }} \cdot \Delta \mathrm{V}\right)$
For an isochoric process: $\Delta \mathrm{V}=0$
$\therefore \quad$ Heat of reaction $=\mathrm{q}_{\mathrm{v}}=\Delta \mathrm{U}$