A student monitors the reaction quotient for a reversible reaction at constant…

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

Problem

A student monitors the reaction quotient

Q

for a reversible reaction at constant temperature and records the following observations: • At

t = 0\,\text{s}

Q = 0.050

. •

Q

increases smoothly and reaches a plateau of

0.150

t = 300\,\text{s}

. • The literature value of the equilibrium constant at this temperature is

K = 0.150

. • At

t = 400\,\text{s}

, the student injects a small amount of product, causing

Q

to spike instantly to

0.300

. • After the spike,

Q

gradually returns to

0.150

. Assume no other disturbances occur. (a) For the time interval

0\,\text{s} < t < 300\,\text{s}

, describe whether the forward or reverse reaction is thermodynamically favored and give the sign of

\Delta G

for the forward reaction. Justify using

Q

and

K

. (b) Explain why

Q

remains constant at

0.150

between

300\,\text{s}

and

400\,\text{s}

. (c) Immediately after the product injection at

400\,\text{s}

, predict the direction of the net reaction and the sign of

\Delta G

for the forward process. Support your answer with reference to the new value of

Q

. (d) Describe the changes in the concentrations of reactants and products as

Q

relaxes back to

0.150

after

400\,\text{s}

Related theory

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