For the exothermic reaction 2CO(g) + O2(g) ⇌ 2CO2(g), which of the following changes will increase the yield of CO2 at equilibrium?
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Correct answer
B. Decreasing the temperature
Principle or equation
Le Chatelier's principle: A system at equilibrium responds to a stress by shifting to counteract it. For an exothermic reaction, decreasing temperature shifts equilibrium to the right, producing more products.
Why this answer is correct
The reaction is exothermic, so heat is a product. Decreasing temperature removes heat, causing the equilibrium to shift to the right to produce more heat, thus increasing CO2 yield. Increasing volume favors the side with more gas moles (reactants: 3 moles vs products: 2 moles), shifting left. A catalyst speeds up both directions equally and does not change equilibrium yield. Removing CO2 would shift right but the question asks for a change that increases yield at equilibrium; removing product does increase yield but it is a continuous removal, not a single change. However, the most direct and standard answer is decreasing temperature.
Example
For N2(g) + 3H2(g) ⇌ 2NH3(g) (exothermic), lowering temperature increases NH3 yield.
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