Thermodynamics is not concerned about.

Options

A. energy changes involved in a chemical reaction
B. the extent to which a chemical reaction proceeds
C. the rate at which a reaction proceeds
D. the feasibility of a chemical reaction

Explanation

To determine which aspect thermodynamics is not concerned about, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Identify the Options**: The question provides four options regarding what thermodynamics is not concerned about. We will evaluate each option.

2. **Evaluate Option A**:
- **Statement**: Energy changes involved in a chemical reaction.
- **Analysis**: According to the first law of thermodynamics, the change in internal energy (ΔU) is equal to the heat added to the system (Q) plus the work done on the system (W). This indicates that thermodynamics is fundamentally concerned with energy changes.
- **Conclusion**: This option is incorrect as thermodynamics is indeed concerned about energy changes.

3. **Evaluate Option B**:
- **Statement**: The extent to which chemical reactions proceed.
- **Analysis**: The Gibbs free energy (G) is related to the equilibrium constant (K) of a reaction. A negative Gibbs free energy indicates that a reaction can proceed spontaneously, which relates to the extent of the reaction. Therefore, thermodynamics does address the extent of reactions.
- **Conclusion**: This option is also incorrect as thermodynamics is concerned with the extent of reactions.

4. **Evaluate Option C**:
- **Statement**: The rate at which the reaction proceeds.
- **Analysis**: The rate of a chemical reaction is a topic covered by chemical kinetics, not thermodynamics. Thermodynamics does not provide information about how fast a reaction occurs; it only provides information about whether a reaction can occur and under what conditions.
- **Conclusion**: This option is correct as thermodynamics is not concerned with the rate of reactions.

5. **Evaluate Option D**:
- **Statement**: The feasibility of chemical reactions.
- **Analysis**: Thermodynamics is indeed concerned with the feasibility of reactions, often assessed through changes in entropy (ΔS) and Gibbs free energy (ΔG). A reaction is feasible if the total entropy change (system + surroundings) is positive.
- **Conclusion**: This option is incorrect as thermodynamics is concerned with the feasibility of reactions.

### Final Answer:
Based on the evaluations, the correct answer is **Option C: The rate at which the reaction proceeds**.