Reversibility and dynamic equilibria
4 marks · NormalThe reversible decomposition of dinitrogen tetroxide to nitrogen dioxide is shown below:
Explain what is meant by 'dynamic' in dynamic equilibrium.
Describe what you would observe in the sealed container when equilibrium has been reached.
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(a) The reactions do not stop; forward and backward reactions continue to happen at the same rate, so particles are still reacting even though no macroscopic change is observed.
(b) There would be no further observable changes; the colour intensity (brown) stays constant, showing concentrations are unchanged.
Common mistakes: Not mentioning reactions continue at equilibrium; Describing no visible changes incorrectly
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Marking points
B1 (a) · 1 mark · States that both forward and reverse reactions continue at equilibrium
B2 (a) · 1 mark · States that rates of the two reactions are equal
B3 (b) · 1 mark · Observation: no further visible change (e.g., colour remains the same)
B4 (b) · 1 mark · Links unchanging colour to unchanging concentration of reactants/products
Worked solution
a) 'Dynamic' means that the reactions continue in both directions at the same rate; particles are always reacting but no overall change occurs in the amounts.
b) When equilibrium is reached, the colour of the mixture (brown) becomes stable and does not change further. This is because the concentrations of the gases stay the same.