For the exothermic reaction 2NO2(g) ⇌ N2O4(g), which of the following changes will increase the yield of N2O4 at equilibrium?
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Correct answer
D. Increasing the pressure
Principle or equation
Le Chatelier's principle: for a reaction with fewer moles of gas on the product side, increasing pressure shifts equilibrium toward the side with fewer gas moles. For an exothermic reaction, increasing temperature shifts equilibrium toward reactants.
Why this answer is correct
The reaction has 2 moles of gas on the left and 1 mole on the right. Increasing pressure favors the side with fewer gas moles, thus increasing N2O4 yield. Increasing temperature favors the endothermic reverse reaction, decreasing yield. Decreasing pressure favors the side with more gas moles (NO2). A catalyst does not shift equilibrium.
Example
In N2(g) + 3H2(g) ⇌ 2NH3(g), increasing pressure increases ammonia yield because the product side has fewer gas moles.
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