For the endothermic reaction CaCO3(s) ⇌ CaO(s) + CO2(g), which of the following changes will increase the yield of CaO at equilibrium?
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Correct answer
A. Increasing the volume of the container
Principle or equation
Le Chatelier's principle states that a system at equilibrium will shift to counteract a stress. For a reaction with gaseous components, increasing the volume decreases the pressure, shifting equilibrium toward the side with more moles of gas. Also, for an endothermic reaction, increasing temperature shifts equilibrium to the products.
Why this answer is correct
The reaction has 1 mole of gas on the product side and 0 moles on the reactant side. Increasing the volume (decreasing pressure) shifts equilibrium to the side with more gas moles, which is the product side, thus increasing the yield of CaO. Decreasing temperature would shift equilibrium to the reactants because the reaction is endothermic. A catalyst does not affect equilibrium position. Adding more solid CaCO3 does not change the equilibrium because the concentration of a pure solid is constant.
Example
For N2O4(g) ⇌ 2NO2(g), increasing volume shifts equilibrium to the side with more gas moles (products).
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