Question

Under which of the following conditions is the relation, $\Delta H=\Delta U+P\Delta V$ valid for a closed system?

• A. Constant pressure
• B. Constant temperature
• C. Constant temperature and pressure
• D. Constant temperature, pressure and composition

Answer 1

The correct option is C

Constant temperature and pressure

We know that $H=U+PV$

$\Delta H=\Delta U+\Delta PV$

$\Delta H=\Delta U+P\Delta V+V\Delta P$

At constant pressure

$\Delta H=\Delta U+P\Delta V$

But $P\Delta V$ = $\Delta$$ngRT$

$\Delta H=\Delta U+\Delta$$ngRT$

At constant temperature

$\therefore$ At constant pressure & temperature