Which of the following reaction will shift in forward direction. When the respective change is made at equilibrium

Options

A. `N_(2)(g)+3H_(2)(g)hArr2NH_(3)(g)` increase in pressure at eq.
B. `H_(2)O(s)hArrH_(2)O(l)` addition of inert gas at constant volume
C. `PCI_(5)(g)hArrPCI_(3)(g)+CI_(2)(g)` addition of inert gas at constant pressure
D. `H_(2)+I_(2)hArr2Hi` increase in temperature

Answer

To determine which of the given reactions will shift in the forward direction when respective changes are made at equilibrium, we can apply Le Chatelier's principle. This principle states that if an external change is applied to a system at equilibrium, the system will adjust itself to counteract that change and restore a new equilibrium.

Let's analyze each option step by step:

### Step 1: Analyze the first reaction
**Reaction:** N₂ + 3H₂ ⇌ 2NH₃
**Change:** Increase in pressure

- **Moles of Reactants:** 1 (N₂) + 3 (H₂) = 4 moles
- **Moles of Products:** 2 (NH₃) = 2 moles

**Conclusion:** When pressure is increased, the equilibrium will shift towards the side with fewer moles of gas. Since there are 4 moles on the reactant side and 2 moles on the product side, the equilibrium will shift in the forward direction (towards the production of NH₃).

### Step 2: Analyze the second reaction
**Change:** Addition of inert gas at constant volume

- Adding an inert gas at constant volume does not change the partial pressures of the reactants or products.

**Conclusion:** There will be no shift in the equilibrium position when an inert gas is added at constant volume.

### Step 3: Analyze the third reaction
**Change:** Addition of inert gas at constant pressure

- When an inert gas is added at constant pressure, the volume of the system increases, which results in a decrease in the partial pressures of the reactants and products.

**Conclusion:** According to Le Chatelier's principle, the equilibrium will shift towards the side with more moles of gas. Since the reactants have 4 moles and the products have 2 moles, the equilibrium will shift in the forward direction.

### Step 4: Analyze the fourth reaction
**Change:** Increase in temperature

- The effect of temperature change on equilibrium depends on whether the reaction is endothermic or exothermic.

**Conclusion:** If the reaction is endothermic, increasing the temperature will shift the equilibrium in the forward direction. If it is exothermic, the equilibrium will shift in the backward direction. Therefore, we cannot definitively predict the shift without knowing the nature of the reaction.

### Final Summary
The reactions that will shift in the forward direction when respective changes are made at equilibrium are:
1. Increase in pressure (first reaction)
2. Addition of inert gas at constant pressure (third reaction)