For the endothermic decomposition of solid calcium carbonate: CaCO3(s) <=> CaO(s) + CO2(g) in a closed container, how will the equilibrium position respond to an increase in total pressure and an increase in temperature?

Answer and explanation

Correct answer: A. Higher pressure shifts equilibrium backward; higher temperature shifts forward

- Forward direction produces 1 mole of gas ();
- Reverse direction produces 0 moles of gas (only solids and ).
- Therefore, increasing pressure shifts the reaction to the left (backward).
- Supplying heat shifts the equilibrium in the endothermic direction to absorb added heat.
- Therefore, increasing temperature shifts the reaction to the right (forward), increasing and the equilibrium yield of .
  1. Step 1: Apply Le Chatelier's principle to pressure changes: Increasing pressure shifts the equilibrium in the direction that produces fewer moles of gas.
  2. Step 2: Apply Le Chatelier's principle to temperature changes: The decomposition of is endothermic ().
Answer
Increasing pressure shifts equilibrium backward (left), while increasing temperature shifts equilibrium forward (right)
Why not the others: 'Increasing pressure shifts forward...' contradicts Le Chatelier's principle; 'Both shift forward' ignores the gas mole disparity; 'Both have zero effect' incorrectly ignores the gaseous product.

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