Hydrogen gas reacts with iodine gas to form hydrogen iodide gas in an equilibrium reaction.
\[ H_2(g) + I_2(g) \rightleftharpoons 2HI(g) \quad \Delta H = +26.5 \, kJ/mol \]
Which changes increase the yield of HI at equilibrium?
- adding a catalyst
- adding more hydrogen gas
- increasing the pressure
- increasing the temperature
A) 1 and 3
B) 1 and 4
C) 2 and 3
D) 2 and 4
▶️ Answer/Explanation
Ans: D
1. Adding a catalyst doesn’t affect equilibrium position, only speeds up the reaction.
2. Adding more hydrogen gas (a reactant) shifts equilibrium to the right (Le Chatelier’s principle), increasing HI yield.
3. Increasing pressure has no effect here as there are equal moles of gas on both sides (2 vs 2).
4. Increasing temperature favors the endothermic reaction (forward reaction is endothermic as ΔH is positive), increasing HI yield.
Therefore, only changes 2 and 4 increase HI yield.
Which statements about the Haber process are correct?
- A high temperature is used because the reaction is slow at room temperature.
- A high pressure is used because there are more moles of gaseous reactants than moles of gaseous product.
- A nickel catalyst is used to increase the rate of reaction.
- An iron catalyst is used to increase the equilibrium yield of ammonia.
A) 1 and 2
B) 1 and 4
C) 2 and 3
D) 4 only
▶️ Answer/Explanation
Ans: A
In the Haber process (N₂ + 3H₂ ⇌ 2NH₃):
1. Correct – High temperature (450°C) increases the rate as the reaction is too slow at room temperature.
2. Correct – High pressure (200 atm) favors the side with fewer gas moles (4 → 2).
3. Incorrect – An iron catalyst is used, not nickel.
4. Incorrect – Catalysts don’t affect equilibrium yield, only the rate.
Therefore, only statements 1 and 2 are correct.
In the Haber process, an equilibrium is established.
\[ \text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \]
The forward reaction is exothermic.
Which change to the reaction conditions will move the position of equilibrium to the left?
A) decreasing the pressure by 100 atm
B) decreasing the temperature by 100 °C
C) adding more nitrogen gas to the mixture
D) removing the iron catalyst
▶️ Answer/Explanation
Ans: A
According to Le Chatelier’s Principle, decreasing pressure will shift the equilibrium to the side with more gas molecules. In this case, the left side has 4 gas molecules (1 N₂ + 3 H₂) while the right has 2 (2 NH₃), so decreasing pressure shifts equilibrium left (option A). Decreasing temperature would favor the exothermic reaction (shift right, B is wrong). Adding more nitrogen would shift equilibrium right (C is wrong). A catalyst doesn’t affect equilibrium position (D is wrong).
Question
Acidified aqueous silver nitrate is added to a test-tube containing aqueous chloride ions.
The test-tube is then left in direct sunlight.
Which row describes the observations and explains what happens to the reaction mixture?
Answer/Explanation
Ans:
D