When `NaNO_3` is heated in a closed vessel, `O_2` is liberated and `NaNO_2` is left behind.

Options

A. addition of `NaNO_2` favours reverse reaction
B. addition of `NaNO_3` favours forward reaction
C. increasing temperature favours forward reaction
D. increasing pressure favours forward reaction

Answer

To solve the problem of what happens when sodium nitrate (NaNO₃) is heated in a closed vessel, we can break it down into a series of steps:

### Step 1: Identify the Reaction
When sodium nitrate is heated, it decomposes into sodium nitrite (NaNO₂) and oxygen gas (O₂). The balanced chemical equation for this reaction is:
\[ 2 \text{NaNO}_3 (s) \rightarrow 2 \text{NaNO}_2 (s) + \text{O}_2 (g) \]

### Step 2: Understand the State of Reactants and Products
In this reaction:
- Sodium nitrate (NaNO₃) and sodium nitrite (NaNO₂) are solids (s).
- Oxygen (O₂) is a gas (g).

### Step 3: Analyze the Effect of Temperature
This reaction is endothermic, meaning it absorbs heat. According to Le Chatelier's principle, if we increase the temperature of an endothermic reaction, the equilibrium will shift to favor the formation of products. Therefore, increasing the temperature will shift the reaction to the right, producing more sodium nitrite and oxygen.

### Step 4: Analyze the Effect of Pressure
In a closed vessel, changing the pressure can affect the equilibrium of the reaction. Since there are fewer moles of gas on the left side (0 moles of gas from solid NaNO₃) compared to the right side (1 mole of gas from O₂), increasing the pressure will shift the equilibrium to the left to favor the side with fewer gas moles, which is the reactants.

### Step 5: Conclusion
- Increasing temperature favors the forward reaction (producing more NaNO₂ and O₂).
- Increasing pressure favors the reverse reaction (producing more NaNO₃).

### Final Answer
When sodium nitrate is heated in a closed vessel, it decomposes into sodium nitrite and oxygen gas. The reaction is endothermic, so increasing temperature favors the forward reaction, while increasing pressure favors the reverse reaction.

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