Question

Consider the reaction exothermic reaction at equilibrium N2(g) + 3H2(g) <$\longrightarrow$>2NH3(g), How many of given changes will result in decrease in number of moles of N2 gas present at new equilibrium.

Answer 1

5

Answer 2

The reaction is: N2(g) + 3H2(g) <=> 2NH3(g) ($\Delta H < 0$, exothermic)

Number of moles of gas: Reactants (1 N2 + 3 H2) = 4 moles; Products (2 NH3) = 2 moles.

A decrease in the number of moles of N2 gas means the equilibrium must shift to the right (towards products). We analyze each change based on Le Chatelier's principle:

1. Increase in temperature: For an exothermic reaction, increasing temperature shifts the equilibrium to the left (endothermic direction). This increases the moles of N2.
2. Decrease volume of container: This increases the total pressure. The equilibrium shifts to the side with fewer moles of gas, which is the product side (right). This decreases the moles of N2.
3. Increase in total pressure: Similar to decreasing volume, this shifts the equilibrium to the side with fewer moles of gas (right). This decreases the moles of N2.
4. Addition of He gas at constant pressure: When an inert gas is added at constant pressure, the total volume increases, and the partial pressures of all reacting gases decrease. The equilibrium shifts towards the side with more moles of gas (left). This increases the moles of N2.
5. Addition of He gas at constant volume: Adding an inert gas at constant volume increases the total pressure but does not change the partial pressures of the reacting gases. The equilibrium is not disturbed. There is no change in the moles of N2.
6. Addition of small amount of H2O(l) in vessel: Ammonia (NH3) is highly soluble in water and forms NH4OH. This effectively removes NH3 from the gas phase. To counteract this removal, the equilibrium shifts to the right to produce more NH3. This decreases the moles of N2.
7. Addition of H2 gas in vessel at constant volume: Increasing the partial pressure of a reactant (H2) shifts the equilibrium to the right to consume the added reactant. This decreases the moles of N2.
8. Removing some mole of NH3: Removing a product (NH3) shifts the equilibrium to the right to replenish the removed product. This decreases the moles of N2.
9. Addition of N2 gas: Increasing the partial pressure of a reactant (N2) shifts the equilibrium to the right to consume the added reactant. This increases the moles of N2.
10. Decrease in total pressure: This shifts the equilibrium to the side with more moles of gas (left). This increases the moles of N2.

The changes that result in a decrease in the number of moles of N2 gas are: (2), (3), (6), (7), and (8). Therefore, there are 5 such changes.