The equilibrium constant `K_(p)` for the reaction `H_(2)(g)+I_(2)(g) hArr 2HI(g)` changes if:

Options

A. the total pressure changes
B. a catalyst is used
C. the amounts of `H_(2) and I_(2)` change
D. the temperature changes

Answer

To determine when the equilibrium constant \( K_p \) for the reaction \( H_2(g) + I_2(g) \rightleftharpoons 2HI(g) \) changes, we need to analyze the factors that influence equilibrium constants.

### Step-by-Step Solution:

1. **Understanding Equilibrium Constant**: The equilibrium constant \( K_p \) is a measure of the ratio of the concentrations (or partial pressures) of products to reactants at equilibrium. For the reaction given, it can be expressed as:
\[ K_p = \frac{(P_{HI})^2}{(P_{H_2})(P_{I_2})} \]

2. **Factors Affecting \( K_p \)**: The equilibrium constant \( K_p \) is primarily influenced by temperature. According to Le Chatelier's principle, changes in concentration, pressure, or the presence of a catalyst do not affect the value of \( K_p \).

3. **Analysis of Options**:
- **Total Pressure Changes**: Changing the total pressure of the system (by changing the volume, for example) does not change \( K_p \) as long as the temperature remains constant.
- **A Catalyst is Used**: The introduction of a catalyst speeds up the rate of reaching equilibrium but does not change the position of equilibrium or the value of \( K_p \).
- **Amount of \( H_2 \) and \( I_2 \) Change**: Changing the amounts of reactants will shift the position of equilibrium but will not change the equilibrium constant \( K_p \).
- **Temperature Changes**: Changing the temperature of the system will change the value of \( K_p \) because it affects the equilibrium position according to the endothermic or exothermic nature of the reaction.

4. **Conclusion**: The only factor that will change the equilibrium constant \( K_p \) for the reaction \( H_2(g) + I_2(g) \rightleftharpoons 2HI(g) \) is a change in temperature.

### Final Answer:
The equilibrium constant \( K_p \) changes if the temperature changes.

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