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QJEEM17Ch60ea: JEE Main 2017 Chemistry - Class 11 JEEM17Ch60ea Solution: An ideal gas undergoes isothermal expansion at constant…

An ideal gas undergoes isothermal expansion at constant pressure. During the process :

Multiple Choice Options

  • A enthalpy increases but entropy decreases.
  • B enthalpy remains constant but entropy increases.
  • C enthalpy decreases but entropy increases.
  • D Both enthalpy and entropy remain constant.

Step-by-Step Verified Solution

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 Δ\Delta U = 0. The enthalpy change of the system in isothermal expansion is also zero as

Δ\Delta H = Δ\Delta U + nR Δ\Delta T = 0 + 0 = 0

The entropy change foe an isothermal process is given by

ΔS=nRln⁡(VfVi)≥0\Delta S = nR\ln \left( {{{{V_f}} \over {{V_i}}}} \right) \ge 0

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