Rate of reaction

Recall

Junior College 1

Multiple Choice

The reaction pathway diagram below illustrates the energies of reactants, products and the transition state of a reaction.

Which expression represents the activation energy of the forward reaction?

• E1 – E2

• E1 – E3

• E2 – E3

• (E1 – E2) – (E2 – E3)

Multiple Choice

The reaction represented by the following equation was carried out.

HCO₂CH₃(aq) + NaOH(aq) → HCO₂Na(aq) + CH₃OH(aq)

Which graph best shows the relationship between [CH3OH(aq)] and t, the time from mixing of the reactants?

Multiple Choice

Na₂S₂O₃ reacts with dilute HCl to give a pale yellow precipitate. If 1 cm³ of 0.1 mol dm^–3 HCl is added to 10 cm³ of 0.02 mol dm^–3 Na₂S₂O₃ the precipitate forms slowly.

If the experiment is repeated with 1 cm³ of 0.1 mol dm^–3 HCl and 10 cm³ of 0.05 mol dm^–3 Na₂S₂O₃ the precipitate forms more quickly.

Why is this?

• The activation energy of the reaction is lower when 0.05 mol dm^–3 Na₂S₂O₃ is used.

• The reaction proceeds by a different pathway when 0.05 mol dm^–3 Na₂S₂O₃ is used.

• The collisions between reactant particles are more violent when 0.05 mol dm^–3 Na₂S₂O₃ is used.

• The reactant particles collide more frequently when 0.05 mol dm^–3 Na₂S₂O₃ is used.

Multiple Choice

In the diagram, curve X was obtained by observing the decomposition of 100 cm³ of 1.0 mol dm^–3 hydrogen peroxide, catalysed by manganese(IV) oxide.

• adding water

• adding some 0.2 mol dm^–3 hydrogen peroxide

• using less manganese(IV) oxide

• lowering the temperature

Multiple Choice

Which solid-line curve most accurately represents the distribution of molecular speeds in a gas at 500 K if the dotted-line curve represents the corresponding distribution for the same gas at 300 K?

Multiple Choice

In the Haber process for the manufacture of ammonia, why is the heterogeneous catalyst iron in a finely divided state?

• to reduce its surface area

• to produce the maximum reduction in the activation energy

• to reduce its loss during the reaction

• to increase its surface area

Multiple Choice

The Boltzmann distribution shows the number of molecules having a particular kinetic energy at constant temperature. If the temperature is decreased by 10 °C, what happens to the size of the areas labelled L, M and N?

• L decreases, M decreases, N decreases

• L decreases, M increases, N decreases

• L increases, M decreases, N decreases

• L increases, M decreases, N increases

Multiple Select

Which statements about the properties of a catalyst are correct?

Select the correct answer(s)

• A catalyst increases the average kinetic energy of the reacting particles.

• A catalyst increases the rate of the reverse reaction.

• A catalyst has no effect on the enthalpy change of the reaction.

Multiple Select

The diagram shows the Maxwell-Boltzmann energy distribution curve for molecules of a mixture of two gases at a given temperature. For a reaction to occur the molecules must collide together with sufficient energy.

Ea is the activation energy for the reaction between the gases. Of the two values shown, one is for a catalysed reaction, the other for an uncatalysed one.

Which statement(s) is correct when a catalyst is used?

• Ea1 uncatalysed reaction fewer effective collisions

• Ea1 catalysed reaction more effective collisio

• Ea2 uncatalysed reaction fewer effective collisions

• Ea2 catalysed reaction more effective collisions

Multiple Select

A student puts 10 cm³ of 0.100 mol dm^–3 sulfuric acid into one test-tube and 10 cm³ of

0.100 mol dm^–3 ethanoic acid into another test-tube. He then adds 1.0 g (an excess) of magnesium ribbon to each test-tube and takes suitable measurements. Both acids have the same starting temperature.

Neither reaction is complete after 2 minutes, but both are complete after 20 minutes. Which statements are correct?

You can select more than 1 answer!

• After 2 minutes, the sulfuric acid is at a higher temperature than the ethanoic acid.

• After 2 minutes, the sulfuric acid has produced more gas than the ethanoic acid.

• After 20 minutes, the sulfuric acid has produced more gas than the ethanoic acid.