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Sulfur dioxide and oxygen react in the gas phase - CIE - A-Level Chemistry - Question 34 - 2017 - Paper 1
Question 34
Sulfur dioxide and oxygen react in the gas phase. $$2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g) \\ \Delta H = -197 \text{ kJ mol}^{-1}$$ Which statements are cor... show full transcript
Worked Solution & Example Answer:Sulfur dioxide and oxygen react in the gas phase - CIE - A-Level Chemistry - Question 34 - 2017 - Paper 1
Step 1
1 Increasing the pressure increases the equilibrium yield of SO3.
Answer
This statement is correct. According to Le Chatelier's principle, increasing the pressure in a reaction will shift the equilibrium position toward the side with fewer moles of gas. In this case, the reaction has 3 moles of gas on the left (2SO2 + 1O2) and 2 moles of gas on the right (2SO3), so increasing the pressure will favor the production of SO3.
Step 2
2 Increasing the temperature lowers the value of the equilibrium constant Kp.
Answer
This statement is incorrect. For an exothermic reaction like this one (as indicated by the negative ΔH), increasing the temperature shifts the equilibrium to the left (toward the reactants). While the equilibrium position may change, the temperature increase actually causes the equilibrium constant Kp to decrease because it favors the endothermic direction (reactants).
Step 3
3 The presence of a vanadium(V) oxide catalyst increases the equilibrium yield of SO3.
Answer
This statement is incorrect. A catalyst speeds up the rate of the reaction but does not affect the position of the equilibrium or the equilibrium yield. Thus, while a vanadium(V) oxide catalyst will help the reaction reach equilibrium faster, it does not increase the overall yield of SO3.