Dinitrogen tetroxide stored in a steel cylinder decomposes at elevated temperature…

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

Problem

Dinitrogen tetroxide stored in a

3.00\,\text{L}

steel cylinder decomposes at elevated temperature according to

\text{N}_2\text{O}_4(g)\rightleftharpoons 2\,\text{NO}_2(g)

350\,\text{K}

the cylinder is found to contain

0.800\,\text{mol}

\text{N}_2\text{O}_4

and

0.400\,\text{mol}

\text{NO}_2

. The value of the equilibrium constant in terms of concentration at this temperature is

K_c = 1.5

. The valve on the cylinder is then cracked open briefly so that

0.100\,\text{mol}

\text{NO}_2

escapes while no

\text{N}_2\text{O}_4

is lost. The cylinder is quickly resealed and the temperature is maintained at

350\,\text{K}

. (a) Calculate the concentrations of

\text{N}_2\text{O}_4

and

\text{NO}_2

in the cylinder immediately *after* the release but *before* any shift toward a new equilibrium has occurred. (b) Determine the value of

Q_c

for the mixture at that moment. (c) Compare

Q_c

with

K_c

and predict the direction in which the net reaction will proceed to re-establish equilibrium. (d) After equilibrium is re-established, will the final concentration of

\text{NO}_2

be greater than, less than, or equal to its concentration *before* the cylinder was vented? Support your answer with quantitative or qualitative reasoning that references the results of parts (a)–(c).

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