Phosgene decomposes according to the equilibrium reaction The natural logarithm of…

CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)

Problem

Phosgene decomposes according to the equilibrium reaction

\mathrm{COCl_2}(g) \rightleftharpoons \mathrm{CO}(g) + \mathrm{Cl_2}(g)

The natural logarithm of the equilibrium constant

K_p

was measured at three temperatures and is reported below:

Temperature ( $\text{K}$ )	ln $K_p$
$400\,\text{K}$	$-1.20$
$500\,\text{K}$	$0.25$
$600\,\text{K}$	$1.50$

(1) Part 1: (a) Determine the sign of

\Delta H^\circ

for the decomposition of phosgene. Support your answer with evidence from the data. (2) Part 2: (b) Rank the approximate magnitudes of

K_p

300\,\text{K}

500\,\text{K}

, and

700\,\text{K}

from smallest to largest. Explain your reasoning without performing numerical calculations. (3) Part 3: (c) A sealed vessel is at equilibrium at

500\,\text{K}

when the temperature is suddenly lowered to

400\,\text{K}

. Before the system has a chance to re-establish equilibrium, state whether

Q

is greater than, less than, or equal to the new

K_p

400\,\text{K}

. Predict the direction in which the system will shift to reach the new equilibrium and justify your answer.

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