Question
During isothermal expansion of an ideal gas, its
A.
internal energy increases
B.
enthalpy decreases
C.
enthalpy remains unaffected
D.
enthalpy reduces to zero
Answer :
enthalpy remains unaffected
Solution :
$$\eqalign{
& {\text{We know that,}} \cr
& H = E + W \cr} $$
Enthalpy = internal energy + pressure × volume
$$\eqalign{
& \,\,\,\,\,H = E + pV \cr
& \Delta H = \Delta E + \Delta \left( {pV} \right) \cr
& \Delta H = \Delta E + \Delta \left( {{n_g}RT} \right)\,\,\left( {\because \,\,pV = nRT} \right) \cr} $$
For isothermal expansion of ideal gas, $$\Delta T = 0$$
$$\therefore \,\,\Delta H = \Delta E$$