Question

On isothermal expansion of ideal gas, its

• A. internal energy increases
• B. enthalpy increases
• C. enthalpy becomes zero on decreasing
• D. enthalpy remains unchanged

Answer 1

Answer: (D)

Isothermal process $dT=0,$
$\Delta E=0$ $H=E+pV$
$\Delta H=\Delta E+p.\Delta V$
where, $\Delta H=$ change in enthalpy
$\Delta E=$ change in internal energy
$p=$ pressure
$\Delta V=$ change in volume during expansion of ideal gas
If $pV=nRT$
$\Delta H=\Delta E+\Delta (nRT)$
$\Delta H=\Delta E+nR.\Delta T$
$\Delta T=0$ $\Delta E=0$ (Isothermal expansion)
Hence, $\Delta H=0$
During isothermal expansion, the enthalpy of ideal gas remains unchanged.