1 A student carries out an initial rates investigation on the reaction below.
From the results, the student determines the rate equation for this reaction:
The table below shows some of the student's results.
i. Complete the table by adding the missing initial rates in the boxes.
[I−(aq)] / mol dm−3 [IO3 −(aq)] / mol [H+(aq)] / mol dm−3 Initial rate / mol
−3
dm dm−3 s−1
Experiment 1 0.015 0.010 0.020 0.60
Experiment 2 0.045 0.010 0.020
Experiment 3 0.060 0.040 0.080
[2]
ii. Calculate the rate constant, k, for this reaction. Include units.
Give your answer to two significant figures.
k = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ units _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ [3]
iii. The student repeats Experiment 1 using 0.020 mol dm−3 methanoic acid, HCOOH(aq) (pKa = 3.75), instead
of 0.020 mol dm−3 HCl(aq) as a source of H+(aq).
Determine the initial rate in this experiment. Show your working.
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, initial rate = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ mol dm−3 s−1 [3]
2(a) Ethyne gas, C2H2, is manufactured in large quantities for a variety of uses.
Much of this ethyne is manufactured from methane as shown in the equation below.
Write an expression for Kc for this equilibrium.
[1]
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, (b) A research chemist investigates how to improve the synthesis of ethyne from methane at a high temperature.
The chemist adds CH4 to a 4.00 dm3 container.
The chemist heats the container and allows equilibrium to be reached at constant temperature. The total gas
volume does not change.
The equilibrium mixture contains 9.36 × 10−2 mol CH4 and 0.168 mol C2H2.
i. Calculate the amount, in mol, of H2 in the equilibrium mixture.
amount of H2 = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ mol [1]
ii. Calculate the equilibrium constant, Kc, at this temperature, including units.
Give your answer to three significant figures.
Kc = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ units _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ [3]
iii. Calculate the amount, in mol, of CH4 that the chemist originally added to the container.
amount of CH4 = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ mol [1]
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, (c) The chemist repeats the experiment three times.
In each experiment the chemist makes one change but uses the same initial amount of CH4.
Complete the table to show the predicted effect of each change compared with the original experiment.
Only use the words greater, smaller or same.
Change Kc Equilibrium amount of Initial rate
C2H2(g) / mol
The container is heated at
constant pressure
A smaller container is
used
A catalyst is added to CH4
at the start
[3]
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From the results, the student determines the rate equation for this reaction:
The table below shows some of the student's results.
i. Complete the table by adding the missing initial rates in the boxes.
[I−(aq)] / mol dm−3 [IO3 −(aq)] / mol [H+(aq)] / mol dm−3 Initial rate / mol
−3
dm dm−3 s−1
Experiment 1 0.015 0.010 0.020 0.60
Experiment 2 0.045 0.010 0.020
Experiment 3 0.060 0.040 0.080
[2]
ii. Calculate the rate constant, k, for this reaction. Include units.
Give your answer to two significant figures.
k = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ units _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ [3]
iii. The student repeats Experiment 1 using 0.020 mol dm−3 methanoic acid, HCOOH(aq) (pKa = 3.75), instead
of 0.020 mol dm−3 HCl(aq) as a source of H+(aq).
Determine the initial rate in this experiment. Show your working.
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, initial rate = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ mol dm−3 s−1 [3]
2(a) Ethyne gas, C2H2, is manufactured in large quantities for a variety of uses.
Much of this ethyne is manufactured from methane as shown in the equation below.
Write an expression for Kc for this equilibrium.
[1]
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, (b) A research chemist investigates how to improve the synthesis of ethyne from methane at a high temperature.
The chemist adds CH4 to a 4.00 dm3 container.
The chemist heats the container and allows equilibrium to be reached at constant temperature. The total gas
volume does not change.
The equilibrium mixture contains 9.36 × 10−2 mol CH4 and 0.168 mol C2H2.
i. Calculate the amount, in mol, of H2 in the equilibrium mixture.
amount of H2 = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ mol [1]
ii. Calculate the equilibrium constant, Kc, at this temperature, including units.
Give your answer to three significant figures.
Kc = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ units _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ [3]
iii. Calculate the amount, in mol, of CH4 that the chemist originally added to the container.
amount of CH4 = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ mol [1]
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, (c) The chemist repeats the experiment three times.
In each experiment the chemist makes one change but uses the same initial amount of CH4.
Complete the table to show the predicted effect of each change compared with the original experiment.
Only use the words greater, smaller or same.
Change Kc Equilibrium amount of Initial rate
C2H2(g) / mol
The container is heated at
constant pressure
A smaller container is
used
A catalyst is added to CH4
at the start
[3]
© OCR 2025. You may photocopy this page. 4 of 31 Created in ExamBuilder
