3.1.5 Kinetics

Question 1

What does collision theory state?

Answer 1

For a chemical reaction to take place, particles must collide with each other with sufficient energy.

Question 2

What happens if collisions are unsuccessful?

Answer 2

A chemical reaction will not take place.

Question 3

What is collision frequency?

Answer 3

The number of collisions per unit time.

Question 4

What happens when collision frequency increases?

Answer 4

The number of particles that collide with energy greater than or equal to the activation energy increases, so the rate of reaction increases.

Question 5

What is activation energy?

Answer 5

The minimum energy requirement in order for a chemical reaction to take place.

Question 6

What is needed for a successful collision to take place?

Answer 6

Particles must collide with energy that is greater than or equal to the activation energy.

Question 7

Why do most collisions not lead to a reaction?

Answer 7

Because particles do not collide with energy that is greater than or equal to the activation energy.

Question 8

What is a catalyst?

Answer 8

A substance that increases the rate of a chemical reaction without being used up.

Question 9

How do catalysts increase the rate of reaction?

Answer 9

By providing an alternative reaction pathway with a lower activation energy.

Question 10

What is the rate of reaction?

Answer 10

The speed at which a chemical reaction takes place.

Question 11

What is rate of reaction measured in?

Answer 11

Moldm^-3 s^-1

Question 12

How do you find the rate of reaction at a point on a curve?

Answer 12

Draw a tangent to the point and the gradient of the tangent is equal to the rate of reaction at that point.

Question 13

How does increasing the temperature affect the rate of reaction?

Answer 13

It increases the rate of reaction

Question 14

Why does increased temperature increase the rate of reaction?

Answer 14

At higher temperatures, the particles have more kinetic energy, so are moving faster. This means they collide more frequently. A higher number of collisions increases the proportion of particles that collide with energy greater than or equal to the activation energy. This increases the rate of reaction.

Question 15

How does increased concentration of reactants affect the rate of reaction?

Answer 15

Increases the rate of reaction

Question 16

Why does increased concentration of reactants increase the rate of reaction?

Answer 16

Increasing the concentration of reactants will increase the rate of reaction, as there is a greater number of reactant particles per unit volume. This means there will be more frequent successful collisions, which increases the chance of particles colliding with energy greater than or equal to the activation energy.

Question 17

How does increased pressure affect the rate of reaction in a gaseous reaction?

Answer 17

Increases the rate of reaction

Question 18

Why does increasing the pressure of a gaseous reaction increase the rate of reaction?

Answer 18

When the pressure is increased, there are more particles per unit volume. This means there will be more frequent successful collisions, which increases the chance of particles colliding with energy greater than or equal to the activation energy. Therefore the rate of reaction increases.

Question 19

How does increased surface area affect the rate of reaction?

Answer 19

Increased rate of reaction

Question 20

Why does increasing the surface area increase the rate of reaction?

Answer 20

When the surface area increases, there are more reactant particles exposed and therefore available to react. Therefore, there will be more frequent collisions between reactants. This increases the chance of particles colliding with energy greater than or equal to the activation energy, which increases the rate of the reaction.

Question 21

What do Maxwell-Boltzmann curves show?

Answer 21

The distribution of energies of molecules at a certain temperature in a gas.
This is because there is variation in the energies of the particles in a gas.

Question 23

What is the most probable energy?

Answer 23

The energy that the most number of molecules have

Question 24

What is the average energy?

Answer 24

The mean energy of all of the molecules in the gas

Question 25

What does the area under the curve represent in maxwell-Boltzmann curve?

Answer 25

The number of moelcules

Question 26

What happens to energy in a collision?

Answer 26

It is transferred from one molecule to another

Question 27

Why is the maxwell-Boltzmann curve asymptotic?

Answer 27

It does not touch the x-axis as there is no maximum energy

Question 28

Why does the maxwell-Boltzmann curve start at the origin?

Answer 28

Because 0 particles have 0 kinetic energy.

Question 29

What happens to a maxwell-Boltzmann curve if temperature increases?

Answer 29

It flattens and shifts to the right The most probable energy and and average energy increase There are more molecules with energy greater than or equal to the activation energy. This shows that the rate of reaction increases.

Question 30

What is a homogenous catalyst?

Answer 30

When the catalyst and the reactants are in the same phase.

Question 31

What is a heterogenous catalyst?

Answer 31

When the catalyst and the reactants are in different phases.

Question 32

What is a phase?

Answer 32

When the substances are chemically uniform. It means the same as ‘state’ in most cases, but thee are some exceptions eg. Water and oil are in different liquid phases.

Question 33

Explain why a catalyst lowering the activation energy increases the rate of reaction?

Answer 33

A lower activation energy means that a greater proportion of molecules in the reaction mixture have energy that is greater than or equal to the activation energy. This means the rate of the catalysed reaction is increased, compared to the uncatalysed reaction.

Question 34

How can catalysts use intermediates?

Answer 34

Sometimes, to lower the activation energy, catalysts form a reactive intermediate, which means that there will be two transition states. The transition states have a lower activation energy to reach than the original reaction pathway. This means a greater proportion of molecules have energy that is greater than or equal to the activation energy, which increases the rate of reaction.

Question 35

What is a transition state?

Answer 35

The stage during a chemical reaction where bonds are constantly broken and reformed.