Changing the concentration of the reactants
2 marks · EasyA graph plots the rate of a chemical reaction against the concentration of a reactant. The graph is a straight line that passes through the origin. Explain what this tells you about the relationship between the rate of the reaction and the concentration of the reactant.
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The rate is directly proportional to the concentration; doubling the concentration doubles the rate.
Also accept: The rate increases in direct proportion to the concentration.; They are directly proportional.
Common mistakes: Saying simply the rate increases without referring to direct proportion.
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Marking points
B1 · 1 mark · States that the rate is directly proportional to concentration OR the line is straight through the origin.
B2 · 1 mark · Mentions that doubling the concentration doubles the rate, or other correct implication of direct proportionality.
Worked solution
Since the graph is a straight line through the origin, the rate of reaction is directly proportional to the concentration of the reactant. If the concentration is doubled, the rate also doubles.