For the exothermic reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), which of the following changes will increase the equilibrium yield of SO3?
Show the answer and explanation
Correct answer
D. Removing SO3 from the reaction mixture
Principle or equation
Le Chatelier's principle: if a system at equilibrium is disturbed, the equilibrium shifts to counteract the disturbance. For an exothermic reaction, increasing temperature shifts equilibrium to the left (reactants). Decreasing pressure shifts equilibrium toward more moles of gas. A catalyst does not shift equilibrium. Removing product shifts equilibrium to the right to produce more product.
Why this answer is correct
Removing SO3 from the mixture decreases the concentration of product, causing the equilibrium to shift to the right to produce more SO3. Increasing temperature favors the endothermic reverse reaction, decreasing SO3 yield. Decreasing pressure favors the side with more gas moles (reactants: 3 moles vs products: 2 moles), decreasing SO3 yield. A catalyst speeds up both forward and reverse reactions equally and does not change equilibrium position.
Example
If SO3 is continuously removed, the reaction will continue to produce more SO3 until reactants are depleted.
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