To analyze the given equilibrium reaction and understand the effect of changes on the system, let's proceed step-by-step:

Reaction:

$\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$

Question 4: Effects of Adding H₂(g)

When additional H₂(g) is added to the system at constant volume, we need to determine how the system will respond. This response is governed by Le Chatelier's Principle, which states that the system will adjust to counteract the change.

1. Increase in $\text{H}_2$ Concentration: Adding $\text{H}_2$ will initially increase the concentration of $\text{H}_2$.

2. Shift in Equilibrium: To counteract the increase in $\text{H}_2$ concentration, the equilibrium will shift to the right (towards the formation of more $\text{NH}_3$).

3. Effect on Concentrations:

   • The concentration of $\text{NH}_3$ will increase as more $\text{NH}_3$ is formed.
   • The concentration of $\text{N}_2$ will decrease as it reacts with the added $\text{H}_2$.

4. Heat Production: Since the reaction is exothermic (produces heat), shifting the equilibrium to the right will release heat energy.

5. Catalyst Effect: $\text{H}_2$ is not a catalyst; it is a reactant. A catalyst would speed up both the forward and reverse reactions without affecting equilibrium concentrations.

Conclusion for Question 4:

Correct Answer: Heat energy will be produced.

Question 5: Effect of Decreasing Total Pressure

When the total pressure of the system is decreased, the system will again respond according to Le Chatelier's Principle:

1. Effect of Pressure Decrease: Decreasing the pressure will cause the system to shift toward the side with more gas molecules to increase pressure.

2. Number of Gas Molecules:

   • Left side (reactants): 1 molecule of $\text{N}_2$ + 3 molecules of $\text{H}_2$ = 4 molecules
   • Right side (products): 2 molecules of $\text{NH}_3$

3. Shift in Equilibrium: To counteract the decrease in pressure, the equilibrium will shift to the left, where there are more gas molecules (4 on the left vs. 2 on the right).

4. Effect on Equilibrium Constant: The equilibrium constant ($K$) depends only on temperature. A change in pressure does not affect $K$ for reactions involving gases.

Conclusion for Question 5:

Correct Answer: The equilibrium will shift to the left, and the value of the equilibrium constant will stay the same.

Summary:

1. Immediate effect after adding $\text{H}_2(g)$: Heat energy will be produced.
2. Effect of decreasing total pressure: The equilibrium will shift to the left, and the value of the equilibrium constant will stay the same.

Additional Questions for Further Understanding:

1. What is Le Chatelier's Principle and how does it apply to chemical equilibria?
2. How does temperature affect the position of equilibrium in an exothermic reaction?
3. What are the different factors that can affect the equilibrium constant $K$?
4. How does the presence of a catalyst affect the rate of reaction and equilibrium?
5. What is the significance of the equilibrium constant $K$ in chemical reactions?

Tip:

When dealing with equilibrium problems, always consider how changes in concentration, pressure, and temperature will affect the system according to Le Chatelier's Principle.