JEE MAIN - Chemistry (2017 - 9th April Morning Slot - No. 23)
An ideal gas undergoes isothermal expansion at constant pressure. During
the process :
enthalpy increases but entropy decreases.
enthalpy remains constant but entropy increases.
enthalpy decreases but entropy increases.
Both enthalpy and entropy remain constant.
Explanation
In an isothermal expansion process, the temperature of the system remains constant throughout the process. Since, for an ideal gas, U depends only on temperature, we have $$\Delta$$U = 0. The enthalpy change of the system in isothermal expansion is also zero as
$$\Delta$$H = $$\Delta$$U + nR$$\Delta$$T = 0 + 0 = 0
The entropy change foe an isothermal process is given by
$$\Delta S = nR\ln \left( {{{{V_f}} \over {{V_i}}}} \right) \ge 0$$
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