When `NaNO_(3)` is heated in a closed vessel, oxygen is liberated and `NaNO_(2)` is left behind. At equilibrium

Options

A. addition of `NaNO_(2)` favour reverse reaction
B. addition of `NaNO_(3)` favours forward reaction.
C. increasing temperature favours forward reacton.
D. decreasing pressure favours reverse reaction.

Answer

To solve the problem, we need to analyze the reaction that occurs when sodium nitrate (NaNO₃) is heated in a closed vessel. The reaction can be represented as follows:

\[ 2 \text{NaNO}_3 (s) \rightarrow 2 \text{NaNO}_2 (s) + \text{O}_2 (g) \]

### Step-by-Step Solution:

1. **Identify the Reaction**:
The reaction involves the decomposition of sodium nitrate (NaNO₃) into sodium nitrite (NaNO₂) and oxygen gas (O₂).

2. **Determine the State of Reactants and Products**:
- Sodium nitrate (NaNO₃) is a solid.
- Sodium nitrite (NaNO₂) is also a solid.
- Oxygen (O₂) is a gas.

3. **Understand the Equilibrium Concept**:
At equilibrium, the rates of the forward reaction (decomposition of NaNO₃) and the reverse reaction (formation of NaNO₃ from NaNO₂ and O₂) are equal.

4. **Apply Le Chatelier's Principle**:
Le Chatelier's principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the equilibrium will shift in a direction that counteracts the change.

5. **Analyze Each Statement**:
- **Statement 1**: Addition of NaNO₂ favors the reverse reaction.
- **Correct**: Increasing the concentration of NaNO₂ (product) will shift the equilibrium to the left (reverse direction) to reduce the concentration of the product.

- **Statement 2**: Addition of NaNO₃ favors the forward reaction.
- **Correct**: Increasing the concentration of NaNO₃ (reactant) will shift the equilibrium to the right (forward direction) to reduce the concentration of the reactant.

- **Statement 3**: Increasing the temperature favors the forward reaction.
- **Correct**: The decomposition of NaNO₃ is endothermic (absorbs heat). Increasing the temperature will favor the forward reaction to produce more products.

- **Statement 4**: Decreasing the pressure favors the reverse reaction.
- **Incorrect**: Decreasing the pressure will favor the side with more gaseous moles. In this case, the forward reaction produces one mole of gas (O₂), while the reverse reaction does not produce any gas. Therefore, decreasing pressure favors the forward reaction.

6. **Conclusion**:
The correct statements are 1, 2, and 3. Statement 4 is incorrect.

### Final Answer:
- Correct Statements: 1, 2, and 3.