Hydrogen and iodine vapour are heated in a sealed glass tube.
H2(g)+I2(g)⇌2HI(g) \mathrm{H_{2}(g) + I_{2}(g) \rightleftharpoons 2HI(g)} H2(g)+I2(g)⇌2HI(g)Iodine vapour is purple. Hydrogen and hydrogen iodide are colourless.
Which observation shows that the mixture has reached dynamic equilibrium?
The purple colour disappears completely.
The purple colour keeps getting darker.
The purple colour fades and then returns.
The purple colour stops changing in intensity.
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.