Question

In a steam boiler, hot gases form a fire transfer heat to water, which vaporizes at constant temperature. In a certain case, the total change in entropy is 2.045 kJ/K in this process when temperature of surroundings is 30°C. What is the increase in unavailable energy due to irreversible heat transfer?

• A. 619.6 kJ
• B. 639.6 kJ
• C. 15.6 kJ
• D. 721.3 kJ

Hint:

Unavailable energy = T\(_0\) \(\times\) \(\Delta S\).
Energy lost due to irreversibility.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Unavailable energy is the energy that cannot be converted to work.
It is related to entropy change and temperature.

Step 2: Key Formula or Approach:
Unavailable energy = T\(_0\) \(\times\) \(\Delta S\).

Step 3: Detailed Explanation:
Given: \(\Delta S\) = 2.045 kJ/K, T\(_0\) = 30°C = 303 K.
Unavailable energy = 303 \(\times\) 2.045 = 619.635 kJ.
This is approximately 619.6 kJ.

Step 4: Final Answer:
The increase in unavailable energy is 619.6 kJ.
Hence, the correct option is (A).