The diagram shows the Boltzmann distribution of energies in a gas. The gas undergoes a reaction with an activation energy, Ea. The peak of the distribution is labelled P. If the same reaction is carried out in the presence of a catalyst, which statement is correct?

• The peak P is at a lower height and the position of Ea moves to the left.

• The peak P is at a lower height and the position of Ea moves to the right.

• The peak P remains at the same height and the position of Ea moves to the left.

• The peak P remains at the same height and the position of Ea moves to the right.

Which row is an example of heterogeneous catalysis?

• Esterification - Sulfuric acid

• The Contact process - Divanadium pentoxide

• Destruction of the ozone layer - Chlorine radicals

• Atmospheric formation of sulfur trioxide - Nitrogen dioxide

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?

• Graph A

• Graph B

• Graph C

• Graph D

In a chemical system the particles involved have a range of energies. This can be shown on a graph called the Boltzmann distribution. Which statement correctly explains the effect of a catalyst on the particles in a chemical system?

• A catalyst enables particles with a lower energy to collide successfully.

• A catalyst increases the number of particles with higher energies.

• A catalyst increases the number of particles with the most probable energy value.

• A catalyst increases the value of the most probable particle energy.

Enzymes are biological catalysts. Many 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.

A chemist puts a sample of dilute aqueous hydrochloric acid into beaker 1. She adds a sample of zinc and measures the rate of production of hydrogen gas. She then puts a different sample of dilute aqueous hydrochloric acid into beaker 2. She adds a different sample of zinc and measures the rate of production of hydrogen gas. The rate of the reaction in beaker 2 is greater than the rate of the reaction in beaker 1. Which factors could help to explain this observation?

• 1 The reaction in beaker 1 has a higher activation energy than the reaction in beaker 2.

• 2 The zinc in beaker 1 is in larger pieces than the zinc in beaker 2.

• 3 The acid in beaker 1 is at a lower concentration than the acid in beaker 2.

Which row correctly describes what happens when the temperature of a chemical reaction is decreased?

• Activation energy (Eₐ) decreases, Number of successful collisions decreases

• Activation energy (Eₐ) decreases, Number of successful collisions increases

• Activation energy (Eₐ) remains the same, Number of successful collisions decreases

• Activation energy (Eₐ) remains the same, Number of successful collisions increases

The Boltzmann distribution for a gas at constant temperature is shown below. If the temperature of the gas is reduced by 10 °C the graph changes shape. What happens to the values of n for the molecular energies X, Y, and Z?

• X higher, Y lower, Z higher

• X higher, Y lower, Z lower

• X lower, Y higher, Z lower

• X lower, Y lower, Z lower

Why does the rate of a gaseous reaction increase when the pressure is increased at a constant temperature?

• More particles have energy that exceeds the activation energy.

• The particles have more space in which to move.

• The particles move faster.

• There are more frequent collisions between particles.

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.