The amount of usable energy that is available for doing work in a system is

Options

A. Enthalpy
B. Free energy
C. Activation energy
D. Spontaneous energy

Answer

To solve the question regarding the amount of usable energy available for doing work in a system, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for the type of energy that is usable for performing work in a system.

2. **Identify Key Terms**: We need to differentiate between total energy and usable energy. Total energy refers to all the energy present in a system, while usable energy is the portion of energy that can be harnessed to perform work.

3. **Analyze the Options**:
- **Enthalpy**: This refers to the total heat content of a system and is not specifically about usable energy.
- **Free Energy**: This is the energy available to do work at constant temperature and pressure. It is indeed the correct term for usable energy.
- **Activation Energy**: This is the energy required to initiate a chemical reaction, not the energy available for work.
- **Spontaneous Energy**: This term is not commonly used in thermodynamics and does not refer to usable energy.

4. **Select the Correct Answer**: Based on the analysis, the correct answer is **Free Energy**. This is the energy that is available to do work in a system.

5. **Conclusion**: The amount of usable energy that is available for doing work in a system is known as **Free Energy**.

### Final Answer:
The amount of usable energy that is available for doing work in a system is **Free Energy**.

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