Question

Given below are two statements:

Statement (I): Internal energy and enthalpy are functions of temperature alone.
Statement (II): Specific heat can vary strongly with temperature and pressure of a substance.

In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Remember that \(u = f(T)\) and \(h = f(T)\) is a special simplification applicable only to ideal gases. Always assume real substances unless "ideal gas" is explicitly stated.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
In classical thermodynamics, the functional dependencies of internal energy (\(u\)), enthalpy (\(h\)), and specific heats (\(c_p, c_v\)) depend on the phase and nature of the substance.

Step 3: Detailed Explanation:
1.

Statement (I): Internal energy and enthalpy are functions of temperature alone only for an ideal gas (known as Joule's Law).
For real gases, liquids, and solids, internal energy and enthalpy depend on pressure and volume/density in addition to temperature.
Therefore, Statement (I) is incorrect in a general thermodynamic context.
2.

Statement (II): The specific heats of real substances are not constant.
They can vary significantly with changes in both temperature and pressure, particularly near phase boundaries or the critical point.
Therefore, Statement (II) is correct.

Step 4: Final Answer:
The correct option is 4, which corresponds to Statement (I) being incorrect but Statement (II) being correct.