A student heats a small amount of white solid ammonium chloride at the bottom of a long test tube. The top of the tube stays cool. After a few minutes, a white solid appears near the top of the tube.
Which explanation is correct?
It turns into a gas without changing, then becomes solid where the tube is cool.
It melts, and the liquid moves up the tube and freezes where the tube is cool.
It breaks down into two gases, which react to re-form it where the tube is cool.
It reacts with oxygen in the air to form a new white solid where the tube is cool.
47 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.