To solve the question regarding the effect of adding an inert gas to a reversible reaction at equilibrium while keeping the volume constant, we can follow these steps:
### Step-by-Step Solution:
1. **Understanding the System**:
- We have a reversible reaction at equilibrium. Let's denote the reactants as A and B, and the product as C.
- The reaction can be represented as:
\[ A + B \rightleftharpoons C \]
2. **Condition of the System**:
- The problem states that we are adding an inert gas to the system while keeping the volume constant.
3. **Effect of Inert Gas Addition**:
- When an inert gas is added to a closed system at constant volume, the total number of moles in the system increases. However, since the volume is unchanged, the concentrations of the reactants and products (A, B, and C) remain the same.
- The concentration of a substance is defined as the number of moles per unit volume. If the volume does not change, then the addition of an inert gas does not change the concentrations of A, B, or C.
4. **Impact on Equilibrium**:
- According to Le Chatelier's principle, if a system at equilibrium is subjected to a change, the system will adjust to counteract that change. However, since the concentrations of the reactants and products are unchanged, the equilibrium position will not shift.
- The only change observed would be an increase in the total pressure of the system due to the added inert gas, but this does not affect the equilibrium concentrations of A, B, or C.
5. **Conclusion**:
- Therefore, when an inert gas is added at constant volume, there is no effect on the equilibrium concentrations of the reactants and products. The equilibrium remains unchanged.
### Final Answer:
Adding an inert gas to a reversible reaction at equilibrium while keeping the volume constant does not affect the equilibrium position or the concentrations of the reactants and products. The total pressure of the system increases, but the equilibrium remains unaffected.
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