CAIE A Level Chemistry 9701 · States of matter
A sealed metal cylinder contains nitrogen gas, .
Using the kinetic theory of gases:
(a) explain why the gas exerts a pressure on the inner walls of the cylinder;
(b) explain why this pressure is steady, even though the gas molecules collide with the walls at irregular intervals;
(c) explain what is meant by the two assumptions of an ideal gas: that the gas particles have zero volume, and that there are no intermolecular forces of attraction between the particles.
7 marks, so the mark scheme is looking for about 7 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.