Rates of Reaction Exam-style MCQs | A-Level Chemistry OCR

Question 1

The equation shows the hydrolysis of a bromoalkane.

RBr + OH^- ➔ ROH + Br^-

The rate equation is rate = k[RBr]

RBr is most likely to be

A

bromomethane

B

2-bromopropane

C

1-bromo-2-methylpropane

D

2-bromo-2-methylpropane

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Question 2

A reactant Q is converted into two products.

Which of these graphs shows that this reaction is first order with respect to Q?

A

graph 1

B

graph 2

C

graph 3

D

graph 4

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Question 3

To determine the activation energy, E_a , for a reaction, a graph was plotted of ln k against 1/T, where k is the rate constant.

The Arrhenius equation is

ln k =−RTEa+ constant

The gradient of the graph is equal to

−Ea

−REa

−TEa

−RTEa

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Question 4

For a given initial reactant pressure, the half-life for a first order gaseous reaction was found to be 30 minutes.

If the experiment were repeated at half the initial reactant pressure, the half-life would be

A

15 minutes

B

30 minutes

C

45 minutes

D

60 minutes

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Question 5

Which statement about the rate determining step of a reaction is correct?

A

It is the fast step

B

It cannot involve a catalyst

C

It does not involve zero order reagents

D

It is always between two first-order reagents

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Question 6

Nitrogen dioxide reacts with carbon monoxide as in the equation below.

NO₂ + CO ➔ NO + CO₂

The mechanism is:

NO₂ + NO₂ ➔ NO + NO₃ Slow

NO₃ + CO ➔ NO₂ + CO₂ Fast

Which expression is the correct rate equation?

A

rate = k[NO₂][CO]

B

rate = k[NO₂]²[CO]

C

rate = k[CO]

D

rate = k[NO₂]²

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Question 7

A student plots ln k (y-axis) against 1/T (in K^-1) for a reaction. The student gets a straight line graph that corresponds to the Arrhenius equation:

ln k =−RTEa+ln A

Which statement is correct?

A

the intercept on the x-axis is ln A

B

the intercept on the y-axis is ln A

C

the slope is E_a

D

the slope is E_a/R

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Question 8

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

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

The gradient has the numerical value of -55,000.

What is the activation energy, in kJ mol^-1?

A

+1.5 × 10^-7

B

+2.22 × 10^-6

C

+6.62

D

+457

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Question 9

The equation for the reaction of ICl and H₂is shown below.

2ICl_(g) + H₂(g) ➔ 2HCl_(g) + I_2(g)

The rate constant k for this reaction is 1.63 × 10^-6 dm³ mol^-1 s^-1.

What is the overall order of the reaction?

A

0

B

1

C

2

D

3

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Question 10

Solutions of two compounds, W and X, react together in the presence of a soluble catalyst, Y, as shown in the equation

2W + X ➔ Z

When the concentrations of W, X and Y are all doubled, the rate of reaction increases by a factor of four.

Which is a possible rate equation for this reaction?

A

rate = k [W]²[X]

B

rate = k [W]²[Y]

C

rate = k [X][Y]

D

rate = k [X][Z]

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Question 11

The rate equation for the hydrogenation of ethene:

C₂H_4(g) + H_2(g) ➔ C₂H_6(g)

is rate = k[C₂H₄][H₂].

At a fixed temperature, the reaction mixture is compressed to triple the original pressure.

What is the factor by which the rate of reaction changes?

A

6

B

9

C

12

D

27

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Question 12

The rate expression for the reaction between X and Y is

rate = k [X]²[Y]

Which statement is correct?

A

the rate constant has units mol^-1 dm³ s^-1

B

the rate of the reaction is halved if the concentration of X is halved and the concentration of Y is doubled

C

the rate increases by a factor of 16 if the concentration of X is tripled and the concentration of Y is doubled

D

the rate constant is independent of temperature

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Question 13

What are the units of the rate constant for a third order reaction?

A

mol dm^-3 s^-1

B

mol^-1 dm^-3 s^-1

C

mol² dm^-6 s^-1

D

mol^-2 dm⁶ s^-1

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Question 14

The results of an investigation of the reaction between P and Q are shown in this table.

The rate equation is: rate = k[P][Q]²

What is the initial concentration of Q in experiment 2?

A

0.167

B

0.333

C

0.408

D

0.612

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