Explaining what's happening
4 marks · NormalA reaction between excess zinc and dilute sulfuric acid is carried out in a conical flask. The total volume of hydrogen gas produced is measured.
State one way the rate of this reaction could be increased without changing the temperature.
Explain your answer to part (a) using collision theory.
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.
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(a) — · must show Increase concentration of acid, Use zinc powder or increase surface area
(b) — · must show More acid particles per volume/more surface area means more frequent collisions, Increases collision rate between reactant particles, More successful collisions per second/reaction is faster
Also accept: Increase concentration of acid; Use powdered zinc
Common mistakes: Suggesting raising temperature; Not linking to collisions
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Identifies a valid way to increase the rate (e.g. increase acid concentration or use powdered zinc/increase surface area)
M1 (b) · 1 mark · Explains that this change increases the number of collisions per second (collision frequency increases)
M2 (b) · 1 mark · Links to more frequent successful collisions (greater chance for productive collisions)
A1 (b) · 1 mark · Correctly states that the reaction rate increases because of more frequent collisions between reactant particles
Worked solution
a) Rate can be increased by increasing the concentration of sulfuric acid or by using powdered zinc (increasing surface area).
b) Increasing the concentration of acid means there are more acid particles in the same volume, so collisions with zinc particles happen more often. Using powdered zinc increases the surface area so there are more places for acid to collide with zinc. Both increase the frequency of successful collisions, so the reaction is faster.