Changing the concentration of the reactants
3 marks · NormalExplain how you can tell from a graph whether the rate of reaction is directly proportional to the concentration of the reactant.
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Also accept: States that if the rate-concentration graph is a straight line through the origin, the relationship is directly proportional
Common mistakes: Only stating 'straight line' without reference to origin; Not mentioning axes/variables
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Marking points
B1 · 1 mark · Mentions that the graph is a straight line.
B2 · 1 mark · States that the straight line passes through the origin (0,0).
B3 · 1 mark · Refers specifically to a graph of rate (y-axis) against concentration (x-axis), or that doubling concentration doubles rate, etc.
Worked solution
If a graph of rate of reaction (y-axis) against concentration (x-axis) is a straight line that passes through the origin (0,0), this shows that the rate is directly proportional to the concentration. This means, for example, that doubling the concentration doubles the rate.