Changing the concentration of the reactants
4 marks · NormalLook at the following graph, which shows the rate of reaction (y-axis, in g/s) against concentration of hydrochloric acid (x-axis, in mol/dm³) for a certain reaction.
Describe the shape and position of the line on the graph.
What does this show about the relationship between the concentration of hydrochloric acid and the rate of reaction?
If the concentration is doubled, what happens to the rate of reaction? Explain your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) The line is straight and passes through the origin (0,0)
(b) The rate is directly proportional to the concentration
(c) If the concentration doubles, the rate of reaction also doubles because they are directly proportional as shown by the straight line through the origin
Common mistakes: Only mentioning line is straight without referring to origin
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly describes that the graph is a straight line through the origin.
B2 (b) · 1 mark · States that rate is directly proportional to concentration.
E1 (c) · 1 mark · States the rate doubles if concentration is doubled.
E2 (c) · 1 mark · Explains this is due to direct proportionality/line through origin.
Worked solution
a) The line is straight and passes through the origin (0,0). b) This shows that the rate of reaction is directly proportional to the concentration. c) If the concentration doubles, the rate also doubles, because the relationship is directly proportional (shown by the straight line through the origin on the graph).