Define internal energy of a gas. Why do we say that internal energy is an exact differential ?

Explanation

**Step-by-Step Solution:**

1. **Definition of Internal Energy:**
- Internal energy, denoted by \( U \), is defined as the total energy possessed by the molecules of a gas. This energy arises from the molecular motion and configuration of the gas molecules.
- The molecular motion includes:
- **Translational Motion:** Movement of molecules from one location to another.
- **Rotational Motion:** Rotation of molecules around their axes.
- **Vibrational Motion:** Oscillation of molecules about their equilibrium positions.
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