Consider the equilibrium reaction:
`4NH_(3((g)))+3O_(2((g)))hArr2N_(2((g)))+6H_(2)O_((g))`
`(DeltaH=-1268KJ)`
Which change will cause the reaction to shift to the right?

Options

A. Increase the temperature
B. Decrease the volume of the container.
C. Add a catalyst to speed up the reaction.
D. None of these

Answer

To determine which change will cause the reaction to shift to the right, we can analyze the given equilibrium reaction and apply Le Chatelier's principle. The reaction is:

\[ 4NH_3(g) + 3O_2(g) \rightleftharpoons 2N_2(g) + 6H_2O(g) \]
with \(\Delta H = -1268 \, \text{kJ}\) indicating that the reaction is exothermic.

### Step-by-Step Solution:

1. **Identify the Reaction Type**:
The reaction is exothermic, meaning it releases heat. According to Le Chatelier's principle, if a system at equilibrium is subjected to a change in temperature, pressure, or concentration, the system will adjust to counteract that change.

2. **Effect of Temperature**:
- **Increase in Temperature**: For an exothermic reaction, increasing the temperature will shift the equilibrium to the left (towards the reactants) because the system will try to absorb the added heat.
- **Decrease in Temperature**: Conversely, decreasing the temperature favors the exothermic direction (to the right, towards the products).

3. **Effect of Pressure**:
- The total number of moles of gas on the left side (reactants) is \(4 + 3 = 7\) moles.
- The total number of moles of gas on the right side (products) is \(2 + 6 = 8\) moles.
- According to Le Chatelier's principle, decreasing the volume (which increases pressure) will shift the equilibrium towards the side with fewer moles of gas. Here, that is the left side, hence it does not favor the forward reaction.

4. **Effect of Concentration**:
- Increasing the concentration of reactants (NH₃ or O₂) will shift the equilibrium to the right (towards the products).
- Decreasing the concentration of products (N₂ or H₂O) will also shift the equilibrium to the right.

5. **Effect of Catalyst**:
- Adding a catalyst does not shift the equilibrium position; it only speeds up the rate at which equilibrium is reached.

### Conclusion:
To shift the equilibrium to the right, the best changes would be:
- Decrease the temperature (since the reaction is exothermic).
- Increase the concentration of reactants (NH₃ or O₂).
- Decrease the concentration of products (N₂ or H₂O).

### Final Answer:
The change that will cause the reaction to shift to the right is **decreasing the temperature** or **increasing the concentration of reactants**.

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