A liquid compound R changes reversibly into a different liquid compound S inside a sealed glass ampoule. At dynamic equilibrium, measurements show 6.0 mmol of R and 4.0 mmol of S.
Which statement correctly predicts what will happen to these amounts if the ampoule is left for longer under the same conditions?
S rises above 4.0 mmol, because the forward reaction is still happening.
S falls below 4.0 mmol, because S is still changing back into R.
R and S rise and fall in turn, because the two reactions take turns.
R stays at 6.0 mmol and S stays at 4.0 mmol, because the two rates are equal.
124 exam-style questions on OCR GCSE Chemistry 5.3 Equilibria, covering 5.3.1 Reversible reactions and dynamic equilibrium and 5.3.2 Changing the position of equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.