A LevelChemistryOCRTopic Questions5. Physical Chemistry & Transition Elements (A Level Only)5.1 Rates, Orders & Arrhenius

Rates, Orders & Arrhenius (OCR A Level Chemistry)

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11 mark

The reaction between iodine and propanone can be catalysed by sulfuric acid. The rate equation shows that this reaction is first order with respect to propanone:

Rate = k [H+] [C3H6O]

Which graph shows that the reaction is first order with respect to propanone?

5-1-q1

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21 mark

Substances W and W react in solution according to the equation.

W + 2X → Y + 2Z

The results of an investigation of the reaction between A and B are shown in this table.

Experiment

Initial [W]
/ mol dm–3

Initial [X]
/ mol dm–3

Initial rate
/ mol dm–3 s–1
1 0.50 0.50 7.0 x 10-4
2 0.50 1.00 To be calculated

 

The reaction is zero order with respect to W and first order with respect to X.

What is the initial rate of experiment 2?

  • 2.8 x 10-3 mol dm–3 s–1

  • 1.4 x 10-3 mol dm–3 s–1

  • 7.0 x 10-4 mol dm–3 s–1

  • 3.5 x 10-4 mol dm–3 s–1

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31 mark

The rate equation for the reaction between X and Y is:

Rate = k [X] [Y]

What are the correct units for the rate constant, k, of this rate equation?

  • mol dm-3 s-1

  • mol2 dm-6 s-1

  •  dm6 mol-2 s-1

  •  dm3 mol-1 s-1

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41 mark

The Arrhenius equation is shown below.

k = Ae-Ea / RT

Which term from the Arrhenius equation has the incorrect units?

  Term Units
A Ea J mol-1
B R J K-1 mol-1
C T K
D e No units

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51 mark

An alternative version of the Arrhenius equation is:

ln space k space equals space fraction numerator negative E subscript straight a over denominator R end fraction space 1 over T space plus space ln space A

Which specific term can be calculated from an Arrhenius plot, shown below, using this equation?

5-1-q5

  • Ea

  • begin mathsize 14px style 1 over T end style

  • R

  • begin mathsize 14px style 1 over R end style

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1
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Using the graph, what is the value of the pre-exponential factor, A, for the decomposition of N2O5?

2N2O5(g) → 4NO(g) + O2(g)

rates-graphs

  • 3.45 s-1

  • 31.5 s-1

  • 1.04 × 105 s-1

  • 4.79 × 1013 s-1

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21 mark

Acidified propanone was added to a solution of iodine. The rate equation is:

rate = k[CH3COCH3][H+]2

The initial rate of reaction is 2.75 x 10-3 mol dm-3

 

CH3COCH3

I2

H+

Initial concentration (mol dm-3)

3.32

0.25

0.73

 

What is the value of the rate constant?

  • 1.55 x 10-3 mol-2 dm6 s-1

  • 1.13 x 10-3 mol-2 dm6 s-1

  • 1.55 x 10-3 mol dm3 s-1

  • 1.13 x 10-3 mol dm3 s-1

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31 mark

The Arrhenius equation can be used to calculate the activation energy of a reaction. The gas constant, R = 8.31 J K-1 mol-1.

bold 1 over bold T K-1

ln k

0.00347

-10.9

0.00336

-9.7

0.00325

-8.5

0.00314

-7.3

0.00305

-6.1

 

What is the activation energy for this reaction to 3 significant figures?

  • 7.62 x 10-4 kJ mol-1

  • -7.62 x 10-4 kJ mol-1

  • 90700 kJ mol-1

  • -90700 kJ mol-1

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41 mark

A series of experiments was carried out on a reaction involving compounds A, B and C and the following results were obtained.

Experiment

Initial concentration of A / mol dm-3

Initial concentration of B / mol dm-3

Initial concentration of C / mol dm-3

Initial rate /
mol dm-3 s-1

1

0.4

0.12

0.42

3.2 x 10-3

2

0.8

0.24

0.42

6.4 x 10-3

3

0.4

0.12

0.21

8.0 x 10-4

4

1.2

0.24

0.84

3.84 x 10-2

 

What is the correct rate equation for this reaction?

  • rate = k[A][C]2

  • rate = k[A]2[B]

  • rate = k[A][B][C]2

  • rate = k[A]2[B][C]

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51 mark

For the reaction between nitric oxide and hydrogen, a possible reaction mechanism is shown below.

Overall: 2NO (g) + 2H2 (g) → N2 (g) + 2H2O (l)

Step 1: 2NO (g) → N2O2 (g)

Step 2: N2O2 (g) + H2 (g) → H2O (l) + N2O (g)

Step 3: N2O (g) + H2 (g) → N2 (g) + H2O (l)

Rate = k[NO]2[H2]

  1. The rate of reaction is halved if [NO] is halved and [H2] is doubled.
  2. The second step is the rate-determining step.
  3. The rate constant is independent of temperature.

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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11 mark

Which concentration–time graph is correct for a reaction that is zero order with respect to a reactant?

A blQswxWs_conc-time-graph-option-a
B SfDyTwrV_conc-time-graph-option-b
C 3Q~Rijan_conc-time-graph-option-c
D juhr5Pl~_conc-time-graph-option-d

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21 mark

The reaction between iodine and propanone can be catalysed by sulfuric acid. The rate equation for this reaction is:

Rate = k [H+] [C3H6O]

Which of the following sets of statements is correct about the order of reaction with respect to each chemical involved? 

  Iodine Propanone Sulfuric acid
A Zero First Second
B First Zero First
C Zero First First
D Zero Second Zero

 

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3
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An investigation into the rate of reaction between compounds A and B was performed. 

                     A + B → Products 

The results from three different experiments carried out at a constant temperature are shown:

Expt. 

Initial concentration of A / mol dm-3

Initial concentration of B / mol dm-3

Initial rate / mol dm-3 s-1

1

0.30

0.50

6.0 x 10-4

2

0.30

0.25

1.5 x 10-4

3

0.60

0.25

3.0 x 10-4

The rate equation for this reaction is rate = k [A] [B]2

What is the value of the rate constant, k? 

  • 2.0 x 10-3

  • 3.2 x 10-2

  • 8.0 x 10-3

  • 2.7 x 10-2

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41 mark

Which rate-concentration graph is correct for a reaction that is second order with respect to a reactant?

ocr-5-1m-q4-option-abcd

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5
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A graph is plotted of ln k against 1/T.

(k = rate constant, T = temperature in K)

The gradient has the numerical value of −45000.

What is the activation energy, in kJ mol−1?

  • 374

  • 374130

  • -374

  • 5.42

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