For the gas-phase reaction, 2NO ` hArr N_(2) + O_(2) : Delta H = -43.5 ` keal. Which one of the following is false for the reaction `N_(2) (g) + O_(2) (g) hArr 2NO(g)`

Options

A. `K_(c) ` is independent of temperature
B. `K_(c)` increases as T decreases
C. `K_(c)` is decreases as T decreases
D. `K_(c)` varies with addition of NO

Answer

To solve the question, we need to analyze the gas-phase reaction and the equilibrium constant (Kc) associated with it. The reaction given is:

\[ 2NO(g) \rightleftharpoons N_2(g) + O_2(g) \quad \Delta H = -43.5 \text{ kcal} \]

This indicates that the reaction is exothermic, meaning it releases heat.

### Step-by-Step Solution:

1. **Identify the Reaction and Its Equilibrium Constant**:
The reaction can be written as:
\[ K_c = \frac{[NO]^2}{[N_2][O_2]} \]
Here, \( K_c \) is the equilibrium constant for the reaction.

2. **Understand the Effect of Temperature on Kc**:
Since the reaction is exothermic (\( \Delta H < 0 \)), according to Le Chatelier's principle:
- If the temperature decreases, the equilibrium will shift to the right (towards the products) to produce more heat, thus increasing \( K_c \).
- If the temperature increases, the equilibrium will shift to the left (towards the reactants), thus decreasing \( K_c \).

3. **Evaluate Each Statement**:
- **Statement 1**: "Kc is independent of temperature."
- This is **false**. \( K_c \) is dependent on temperature.
- **Statement 2**: "Kc increases as temperature decreases."
- This is **true** for an exothermic reaction.
- **Statement 3**: "Kc decreases as temperature decreases."
- This is **false**. \( K_c \) actually increases as temperature decreases for exothermic reactions.
- **Statement 4**: "Kc varies with addition of NO."
- This is **false**. The addition of a reactant or product does not change \( K_c \); it only shifts the position of equilibrium.

4. **Conclusion**:
The false statements regarding the reaction are:
- Kc is independent of temperature.
- Kc decreases as temperature decreases.
- Kc varies with addition of NO.

Thus, the answer to the question is that statements 1, 3, and 4 are false.