AS
Answers

Extension teacher notes questions Answers to examination-style
1 (a) (i) graph starts at origin graph skewed to left and has decreasing gradient to maximum graph after maximum decreases in steepness, never touches x-axis, levels out less than 5 mm from x-axis (b) minimum energy to start a reaction (c) molecules gain energy when they collide with each other (d) decreases reaction goes by an alternative route which has a lower Ea (therefore more molecules have energy >Ea) 2 (a) the minimum energy required for a reaction to occur (b) axes labelled: y: number (or fraction or %) of molecules; x: energy curve starts at origin skewed to right approaches x-axis as an asymptote 1 1 1 1 1 1 1 1 1 1

Chemistry

Chapter 8

Marks Examiner’s tips
You must remember to do all these things. This is worth 3 marks here. Remember that the curve has a decreasing gradient on the left. It is not ‘bell-shaped’.

When two particles collide, one gains energy and the other loses energy. In this way particles pass on energy. A catalyst is a substance that speeds up the reaction and is unchanged at the end. It works by providing an alternative route of lower activation energy.

1 1 The question talks about molecules so don’t label the axis atoms! 1 1 1 1

A curve that levels off >10% of max. peak height or a curve that crosses the energy axis will not score this last mark. Curve must not cross T1 curve twice. This can also be shown on a correctly labelled diagram. You could also say that the orientation may be wrong. Alternatively you can refer to an increase in the concentration or a reduction in the volume. This mark is not allowed if implied that more collisions come from a temperature increase.

second curve displaced to the left and peak higher many fewer molecules have E > Ea (c) molecules do not have enough energy increase the pressure

1 1 1 1 1 1