Kinetics

Question 1

Define the term activation energy, Ea

Answer 1

The minimum energy needed for a reaction to occur

Question 2

How does a catalyst increase the rate of reaction?

Answer 2

Provides an alternative reaction pathway with a lower activation energy

Question 3

What is a catalyst?

Answer 3

A substance which increases the rate of a reaction without being used up overall

Question 4

What are the axis labels in the Boltzmann distribution?

Answer 4

x-axis: (kinetic) energy
y-axis: number of particles

Question 5

Using the Boltzmann distribution, why does increasing the temperature have a large impact on rate of reaction?

Answer 5

Many more particles have energy greater than the activation energy, so there are more frequent successful collisions.

Question 6

Using the Boltzmann distribution, why does increasing the concentration or pressure lead to a higher rate of reaction?

Answer 6

There are more particles per unit volume, so there are more frequent successful collisions

Question 7

What is represented by the area under the curve in the Boltzmann distribution?

Answer 7

The total number of particles

Question 8

Answer 8

B

Question 9

If the temperature of a gas is increased, how does the peak of the Boltzmann distribution move?Down and to the right

Answer 9

Down and to the right

Question 10

Answer 10

D

Question 11

Answer 11

D

Question 12

Do all collisions lead to a reaction? Explain your answer

Answer 12

No. Most collisions do not occur with energy above the activation energy

Question 13

Answer 13

HBr is used up in step 1 and then regenerated in step 2

Question 14

In terms of the Boltzmann distribution, explain how a catalyst increases the rate of reaction.

Answer 14

A catalyst lowers the activation energy, so more particles have energy over the activation energy, so there are more frequent successful collisions.

Question 15

Suggest why a solid catalyst is often in the form of a powder

Answer 15

This increases the surface area so there are more frequent successful collisions

Question 16

From this graph of volume of gas produced in a reaction vs time, how would you measure the initial rate?

Answer 16

Draw a tangent at time t=0, and measure the gradient. This is equal to the rate.

Question 17

This graph is for the volume of hydrogen produced when 100 cm3 1 mol dm-3 HCl reacts with excess Mg. How will the initial gradient and final volume change if 50 cm3 2 mol dm-3 HCl is used?

Answer 17

Initial gradient is steeper, total volume produced is the same.

Question 18

This graph is for the volume of hydrogen produced when 100 cm3 1 mol dm-3 HCl reacts with excess Mg. How will the initial gradient and final volume change if 50 cm3 1 mol dm-3 HCl is used?

Answer 18

Initial gradient is the same, final volume is half.

Question 19

Answer 19

C

Question 20

Why does the Boltzmann distribution start at the origin?

Answer 20

No particles have zero energy.