Reaction kinetics Revision

Which of the following factors can affect the value of the activation energy of a reaction?

1. the presence of a catalyst

2. changes in temperature

3. changes in the concentration of the reactants

• 1 only

• 1 and 2 only

• 3 only

• 1,2, and 3

When the pressure of a fixed mass of gaseous reactants is raised at a constant temperature, the rate of reaction increases.

Which of the following statements explain this observation?

(You can choose more than 1 answer)

• rasing the pressure lowers the activation energy

• more molecules have energy greater than the activation energy at the higher pressure

• More collisions occur per second when the pressure is increased

What is the main reason for the increase in reaction rate with increasing temperature?

• The activation energy decreases

• The activation energy increases

• The molecules collide more frequently

• More molecules have an energy greater than the activation energy

Why does a mixture of hydrogen gas and bromine gas react together faster at a temperature of 500K than it does at temperature of 400K?

(You can choose more than 1 answer)

• A higher proportion of effective collisions occurs at 500K

• The activation energy of the reaction is lower at 500K

• Hydrogen and bromine molecules collide more frequently at 500K

The distribution of molecular energies in a sample of a gas at a given temperature is shown bỵ the graph below. If the temperature is increased, what will happen to the position of point X?

• Fewer molecules possess the most probable energy value so X will shift to the right.

• Fewer molecules possess the most probable energy value so X will shift to the left.

• More molecules possess the most probable energy value so X will shift to the right.

• The position of X will stay the same but the area under the distribution curve increases

The dotted-line curve on each graph below represents the corresponding distribution for a gas at 300K. Which solid-line curve most accurately represents the distribution of molecular energies?

• 
• 
• 
• 

The diagram shows a reaction pathway for an endothermic reaction. Which arrow represents the activation energy for the forward reaction?

• A

• B

• C

• D

The diagram below represents, for a given temperature, the Boltzmann distribution of the kinetic energy of the molecules in a mixture that react slowly together without a catalyst.

The activation energy for the reaction, Ea, is marked for the uncatalysed reaction.

What would be the position of Ea be if the reaction took place with an effective catalyst?

• A

• B

• C

• D

The diagram shows a Boltzmann distribution of molecular energies for a gaseous mixture. The distribution has a peak, labelled Q 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.