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CAIE A-Level Chemistry AS 8.2 Temperature Rate and Activation Energy Questions

Practise using activation energy and Boltzmann distributions to explain how temperature changes reaction rate.

Exam points

define activation energy as the minimum collision energy needed for a reaction to occur
sketch the lower, broader and right-shifted Boltzmann curve produced by increasing temperature
link the larger area above EA to a higher frequency of effective collisions and a faster reaction

Covered syllabus points

8.2.1—Activation energy, EA 8.2.2—Sketch and use the Boltzmann distribution 8.2.3—In terms both of the Boltzmann distribution

[Maximum number: 1]

For a certain endothermic reaction, the activation energy is numerically equal to twice the enthalpy change of reaction.

Which reaction pathway diagram is correct for this reaction?

A

Figure for Question 1 — CAIE A-Level Chemistry AS — Option A

B

Figure for Question 1 — CAIE A-Level Chemistry AS — Option B

C

Figure for Question 1 — CAIE A-Level Chemistry AS — Option C

D

Figure for Question 1 — CAIE A-Level Chemistry AS — Option D

[Maximum number: 1]

The diagram shows the Boltzmann distribution of the energy of gaseous molecules at a particular temperature.

Figure for Question 2 — CAIE A-Level Chemistry AS

Which statement is correct?

A

If the temperature of the gas is raised, the height of the maximum of the curve increases.

B

If the temperature of the gas is raised, the maximum of the curve moves to the right.

C

The length of the line labelled X shows the activation energy for the reaction.

D

The length of the line labelled Y shows the enthalpy change of the reaction.

[Maximum number: 1]

The diagram shows the Boltzmann distribution for one mole of a gas. The gas takes part in a reaction with an activation energy, $E_{a}$ .

Figure for Question 3 — CAIE A-Level Chemistry AS

Which statement correctly describes the effect of an increase in temperature?

A

Peak P will be higher and fewer molecules will have energy $>E_{\mathrm{a}}$ .

B

Peak P will be higher and more molecules will have energy $>E_{\mathrm{a}}$ .

C

Peak P will be lower and fewer molecules will have energy $>E_{\mathrm{a}}$ .

D

Peak P will be lower and more molecules will have energy $>E_{\mathrm{a}}$ .

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