The synthesis of ammonia is given as:
`N_(2)(g)+3H_(2)(g) hArr 2NH_(3)(g), DeltaH^(ɵ)=-92.6 kJ mol^(-1)` given `K_(c)=1.2` and temperature `(T)=375^(@)C`
On increasing the temperature, the value of equilibrium constant `K_(c)`

Options

A. Increases
B. Decreases
C. Remain unchanged
D. Cannot be predicted

Explanation

To solve the question regarding the effect of temperature on the equilibrium constant \( K_c \) for the synthesis of ammonia, we can follow these steps:

### Step 1: Understand the Reaction
The synthesis of ammonia is represented by the following equilibrium reaction:
\[ N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) \]
This reaction has a negative enthalpy change (\( \Delta H^{\circ} = -92.6 \, \text{kJ mol}^{-1} \)), indicating that it is exothermic.

### Step 2: Write the Expression for \( K_c \)
The equilibrium constant \( K_c \) for this reaction can be expressed as:
\[ K_c = \frac{[NH_3]^2}{[N_2][H_2]^3} \]

### Step 3: Apply Le Chatelier's Principle
According to Le Chatelier's principle, if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium will shift to counteract the change. In this case, increasing the temperature will disturb the equilibrium.

### Step 4: Determine the Direction of the Shift
Since the reaction is exothermic (releases heat), increasing the temperature will favor the endothermic direction, which is the reverse reaction:
\[ 2NH_3(g) \rightleftharpoons N_2(g) + 3H_2(g) \]
This means that the equilibrium will shift to the left, resulting in a decrease in the concentration of \( NH_3 \) and an increase in the concentrations of \( N_2 \) and \( H_2 \).

### Step 5: Analyze the Effect on \( K_c \)
As the equilibrium shifts to the left, the concentration of \( NH_3 \) decreases while the concentrations of \( N_2 \) and \( H_2 \) increase. Since \( K_c \) is dependent on the concentrations of the reactants and products at equilibrium, a decrease in the concentration of \( NH_3 \) and an increase in the concentrations of \( N_2 \) and \( H_2 \) will result in a decrease in the value of \( K_c \).

### Conclusion
Thus, on increasing the temperature, the value of the equilibrium constant \( K_c \) decreases.

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