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 can analyze the factors that influence the equilibrium constant.

### Step-by-Step Solution:

1. **Understanding the Reaction:**
The given reaction involves hydrogen gas (\( H_2 \)) and iodine gas (\( I_2 \)) reacting to form hydrogen iodide gas (\( HI \)). The equilibrium constant \( K_p \) is expressed in terms of the partial pressures of the gases involved.

2. **Expression for \( K_p \):**
The equilibrium constant \( K_p \) for the reaction can be expressed as:
\[ K_p = \frac{(P_{HI})^2}{(P_{H_2})(P_{I_2})} \]
where \( P_{HI} \), \( P_{H_2} \), and \( P_{I_2} \) are the partial pressures of \( HI \), \( H_2 \), and \( I_2 \) respectively.

3. **Factors Affecting \( K_p \):**
- **Change in Temperature:** The value of \( K_p \) is dependent on temperature. If the temperature changes, \( K_p \) will change according to whether the reaction is endothermic or exothermic.
- **Change in Total Pressure:** Changing the total pressure does not affect \( K_p \). While it may shift the position of equilibrium, it does not change the numerical value of the equilibrium constant.
- **Use of a Catalyst:** The introduction of a catalyst speeds up the rate of reaction but does not change the equilibrium constant \( K_p \).
- **Change in Concentration of Reactants or Products:** Altering the amounts of \( H_2 \) or \( I_2 \) will shift the equilibrium position but will not change the value of \( K_p \).

4. **Conclusion:**
The only factor that changes the value of \( K_p \) is temperature. Therefore, the correct answer to the question is that \( K_p \) changes if the temperature is changed.

### Final Answer:
The equilibrium constant \( K_p \) for the reaction \( H_2(g) + I_2(g) \rightleftharpoons 2HI(g) \) changes if the **temperature** is changed.

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