AIIMS 2006 Chemistry Entropy Assertion Reason Question

To address the question, let’s analyze both the assertion and the reason in detail.

Assertion:

Water in liquid state is more stable than ice at room temperature.

At room temperature (approximately 25°C or 298 K), the energy state of water in its liquid form is lower than that of ice. This is primarily due to the kinetic energy of water molecules, which allows for more movement and interactions compared to the fixed structure of ice. In thermodynamic terms, the stability of a phase is often associated with its Gibbs free energy ($G$), which can be expressed as:

$$G = H - TS$$

where:

• $H$ is the enthalpy,
• $T$ is the temperature in Kelvin,
• $S$ is the entropy.

At room temperature, the liquid state of water has a lower Gibbs free energy compared to ice, indicating that it is the more stable phase.

Reason:

Water in liquid form has higher entropy than ice.

Entropy ($S$) is a measure of disorder in a system. In the case of water, the liquid state is indeed characterized by higher entropy compared to ice. This is because the molecules in the liquid can move more freely, resulting in a greater number of accessible microstates. For ice, the molecules are arranged in a structured lattice, leading to lower entropy.

The relationship between entropy and Gibbs free energy indicates that systems tend to favor states with higher entropy at a given temperature. Therefore, the reason given is correct and directly supports the assertion.

Conclusion:

Since both the assertion and the reason are true, and the reason correctly explains why the assertion is true, the correct answer is:

A) if both assertion and reason are true and reason is the correct explanation of the assertion.

Clarification of Other Options:

• B) is incorrect because while both statements are true, the reason does indeed provide the correct explanation for the assertion.
• C) is incorrect as both the assertion and the reason are true.
• D) is incorrect because both statements are true.

Additional Concepts:

Understanding the concept of entropy and its implications is crucial in thermodynamics. The second law of thermodynamics also states that the total entropy of an isolated system can never decrease over time, which supports the idea that processes tend to favor states of higher entropy.

In summary, the assertion that liquid water is more stable than ice at room temperature aligns with the principle that higher entropy corresponds to greater stability.