Rate of Reaction - AS Level Exercise

Which of the following factors can affect the value of the activation energy of a reaction? (you can choose more than one answer)

• the presence of a catalyst

• changes in temperature

• changes in the concentration of the reactants

• 1, 2, and 3 are correct

• 1 and 2 only are correct

• 2 and 3 only are correct

• 1 only is correct

The Boltzmann distribution is shown for a sample of gas at an initial temperature, T₁. The sample of gas was heated to temperature, T₂. What is the correct distribution for the higher temperature, T₂?

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The diagram shows a Boltzmann distribution of molecular energies for a gaseous mixture. The distribution has a peak, labelled P on the diagram. What happens when the temperature of the mixture increases?

• The height of the peak P, decreases and the activation energy moves to the left.

• The height of the peak P, decreases and the activation energy moves to the right.

• The height of the peak P, decreases and the activation energy does not change

• The height of the peak P, increases and the activation energy moves to the left.

The diagram shows a Boltzmann distribution of molecular energies for a gaseous mixture. The distribution has a peak, labelled P on the diagram. What happens when an effective catalyst is added to the mixture?

• The height of the peak decreases and the activation energy moves to the right.

• The height of the peak decreases and the activation energy moves to the left.

• The height of the peak remains the same and the activation energy moves to the right.

• The height of the peak remains the same and the activation energy moves to the left.

Which statement about E_a1 is correct?

• E_a1 corresponds to a catalysed reaction with fewer effective collisions than the uncatalysed reaction.

• E_a1 corresponds to an uncatalysed reaction with fewer effective collisions than the catalysed reaction.

• E_a1 corresponds to a catalysed reaction with a greater number of effective collisions than the uncatalysed reaction.

• E_a1 corresponds to an uncatalysed reaction with a greater number of effective collisions than the catalysed reaction.

• higher temperature=P; presence of catalyst=X

• higher temperature=P; presence of catalyst=Y

• higher temperature=Q; presence of catalyst=X

• higher temperature=Q; presence of catalyst=Y

Which diagrams correctly show the effect of the following changes made separately and independently?

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Hydrogen ions catalyse the hydrolysis of esters. Which statement is correct?

• The hydrogen ions act as a heterogeneous catalyst.

• The hydrogen ions are in the same phase as the reactants.

• The hydrogen ions are used up in the reaction.

• The hydrogen ions have no effect on the activation energy of the reaction.

Enzymes are biological catalysts. May enzymes show specificity. An example of an enzyme which shows specificity is glucokinase. Glucokinase is involved in the metabolism of glucose.

What does specificity mean in this context?

• Glucokinase is most effective as a catalyst over a narrow pH range.

• Glucokinase is most effective as a catalyst over a narrow range of temperatures.

• Glucokinase only operates on a narrow range of substrate molecules.

• Glucokinase provides an alternative route for the reactions it catalyses.