When gas in a vessel expands, it thermal energy decreases. The process involved is

Options

A. Isobaric
B. Isochoric
C. Isothermal
D. Adiabatic

Answer

To determine the type of process involved when a gas in a vessel expands and its thermal energy decreases, we can analyze the characteristics of different thermodynamic processes. Here’s a step-by-step solution:

### Step 1: Understand the Types of Processes
1. **Isobaric Process**: This is a process that occurs at constant pressure. In this case, the gas can do work on the surroundings, and heat can be exchanged, but the internal energy may not necessarily decrease.

2. **Isochoric Process**: This process occurs at constant volume. Since the volume does not change, the gas cannot do work on the surroundings. Any heat added or removed will directly change the internal energy.

3. **Isothermal Process**: In this process, the temperature remains constant. For an ideal gas, this means that the internal energy remains constant as well, as internal energy is a function of temperature.

4. **Adiabatic Process**: This is a process in which no heat is exchanged with the surroundings. If a gas expands adiabatically, it does work on the surroundings, and since there is no heat input, the internal energy decreases, leading to a drop in temperature.

### Step 2: Analyze the Given Scenario
In the scenario provided, the gas expands, and its thermal energy (internal energy) decreases. This indicates that work is being done by the gas, and there is no heat being added to compensate for the energy lost.

### Step 3: Identify the Correct Process
Given that:
- The gas expands (doing work).
- The internal energy decreases (indicating that energy is being used for work rather than being compensated by heat).

The process that best fits this description is the **adiabatic process**.

### Conclusion
When a gas in a vessel expands and its thermal energy decreases, the process involved is **adiabatic**.

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