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How Far? The Extent of Chemical Change · Paper 2 — Free Chemistry HL Practice Questions

1ChallengeSAQ-LCalculating equilibrium constants (Kc)7 marksPaper 2~11 min

The esterification reaction between ethanol and ethanoic acid reaches equilibrium in a closed system:

\text{C}_2\text{H}_5\text{OH}(l) + \text{CH}_3\text{COOH}(l) \rightleftharpoons \text{CH}_3\text{COOC}_2\text{H}_5(l) + \text{H}_2\text{O}(l)

A student prepares a mixture by adding

0.500\,\text{mol}

of ethanol and

0.500\,\text{mol}

of ethanoic acid to a

1.00\,\text{dm}^3

flask. The flask is sealed and allowed to reach equilibrium at

298\,\text{K}

. At equilibrium, the concentration of ethyl ethanoate is

0.333\,\text{mol}\,\text{dm}^{-3}

(a)

Calculate the equilibrium constant,

K_c

, for this reaction at

298\,\text{K}

. [3 marks]

(b)

Explain why

K_c

has no units for this reaction. [2 marks]

(c)

When the experiment is repeated at

350\,\text{K}

K_c

decreases to

3.2

. Deduce and explain whether the forward reaction is exothermic or endothermic. [2 marks]

Solutions

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