Question

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

• 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 .

Answer 1

The Correct Option is D

The problem at hand involves understanding the behavior of an ideal gas during an isothermal and isobaric process.

Concept Explanation:

In thermodynamics, the study of heat energy transfer, there are several processes that describe how a gas expands or contracts under various conditions. Two of these processes are defined by constant temperature and constant pressure:

• Isothermal Process: This is a process where the temperature of the gas remains constant. According to the ideal gas law, PV = nRT (where P is pressure, V is volume, n is the number of moles, R is the universal gas constant, and T is temperature), if T remains constant, any change in volume V or pressure P has to be such that their product also remains constant.
• Isobaric Process: This is a process where the pressure of the gas remains constant.

Analysis of the Given Situation:

In this scenario, the process described is both isothermal (constant temperature) and isobaric (constant pressure). Let's analyze each part of the thermodynamic properties:

1. Enthalpy: The enthalpy (H) of an ideal gas depends primarily on its temperature. Since the temperature is constant in an isothermal process, the enthalpy remains constant.
2. Entropy: Entropy (S), a measure of disorder, generally increases with more available volume for the gas particles to occupy. However, since both pressure and temperature are constant, any change in volume does not lead to change in entropy in this context. The entropy remains at equilibrium.

Conclusion:

Considering the conditions stated in the question (isothermal and isobaric processes for an ideal gas), both the enthalpy and entropy remain constant.

Therefore, the correct answer is: Both enthalpy and entropy remain constant.