The high-temperature production of sulfur trioxide is an important step in the…

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

Problem

The high-temperature production of sulfur trioxide is an important step in the industrial synthesis of sulfuric acid. Consider the reaction

2\,\text{SO}_2(g)+\text{O}_2(g)\rightleftharpoons2\,\text{SO}_3(g)\qquad(T=800\,\text{K})

At this temperature,

K_c=4.5\times10^2

. An engineer introduces the following initial concentrations into a

5.00\,\text{L}

reaction vessel at

800\,\text{K}

Species	Initial concentration
$\text{SO}_2$	$0.200\,\text{mol L}^{-1}$
$\text{O}_2$	$0.100\,\text{mol L}^{-1}$
$\text{SO}_3$	$0.350\,\text{mol L}^{-1}$

(a) Calculate the reaction quotient

Q_c

for the mixture immediately after the gases are combined. (b) Compare

Q_c

with

K_c

and determine the direction in which the net reaction proceeds to establish equilibrium. Explain your reasoning. (c) On qualitative concentration-time axes, sketch or describe how the concentrations of

\text{SO}_2

\text{O}_2

, and

\text{SO}_3

change until equilibrium is reached. Clearly indicate which curves correspond to which species and how their slopes evolve as equilibrium is approached.

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