Changing the surface area of the reactants
2 marks · EasyTwo pieces of magnesium ribbon, A and B, have the same mass. Ribbon B is cut into 4 equal shorter pieces. Both are added to separate beakers with the same volume and concentration of hydrochloric acid at the same temperature.
Ribbon A takes 200 seconds to finish reacting. Estimate how the time taken for Ribbon B to finish reacting compares to A, and explain your reasoning.
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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Ribbon B will finish reacting in less time than Ribbon A, because cutting increases surface area and reaction rate.
Also accept: Takes less than 200 seconds; Shorter time than 200 seconds
Common mistakes: Thinks reaction takes longer; Says no change
Show mark scheme and worked solution
Marking points
M1 · 1 mark · States or estimates that Ribbon B takes less time to react than Ribbon A.
M2 · 1 mark · Explains this is because higher surface area increases rate of reaction.
Worked solution
Cutting Ribbon B increases the surface area exposed to the acid.
This increases the rate, so Ribbon B finishes in less than 200 seconds.