1.5 Kinetics

Question 1

Define what is meant by the reaction rate.

Answer 1

The change in concentration of a reaction or product over time.

Question 2

How to calculate reaction rate.

Answer 2

rate of reaction =

amount of reactant used or product formed / time

Question 3

What is the collision theory?

Answer 3

(see page 42 in the revision guide)

Question 4

Define activation energy.

Answer 4

The minimum amount of kinetic energy that particles need to collide to start a reaction.

Question 5

Draw an enthalpy profile diagram.

Answer 5

(see page 42 in the revision guide)

page 1 in the chemrevise revision guide

Question 6

What is a Maxwell-boltsmann distribution? Draw a general one as a graph.

Answer 6

(see page 43 in the revision guide)

page 1 in the chemrevise revision guide

Question 7

What four factors effect the rate of reaction? And how?

Answer 7

• Temperature
• Concentration
• Pressure
• Catalyst

(see page 44 in the revision guide)

Question 8

What three methods can you use to measure the rate of reaction?

Answer 8

• Timing how long a precipitate takes to form.
• Measuring a decrease in mass.
• Measuring the volume of gas given off.

(see page 45 in the revision guide)

Question 9

Describe a dynamic equilibrium.

Answer 9

(see page 47 in the revision guide)

Question 10

State Le Chatelier’s principle.

Answer 10

If a reaction at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will move to counteract the change.

(see page 47 and 48 in the revision guide)

Question 11

Do catalysts affect the position of equilibrium?

Answer 11

No.

The cannot increase yield, but they do mean equilibrium is reached faster.

Question 12

Write the expression for equilibrium constant.

Answer 12

(see page 50)

Question 13

Answer the question bottom of page 50.

Answer 13

Get it right?

Question 14

Answer the question on top of page 51.

Answer 14

Get it right?

Question 15

How does temperature change alter Kc?

Answer 15

(see page 51 in the revision guide)

Question 16

What is oxidation in terms of electrons?

Answer 16

A loss of electrons.

Question 17

What is reduction in terms of electrons?

Answer 17

A gain of electrons.

Question 18

What is an oxidising agent?

Answer 18

It accepts electrons and gets reduced.

see page 52 in the revision guide for an example

Question 19

What is a reducing agent?

Answer 19

It donates electrons and gets oxidised.

see page 52 in the revision guide for an example

Question 20

What are the 7 rules for assigning oxidation states?

Answer 20

(see page 52 in the revision guide)

Question 21

How do Roman numerals show oxidation states?

Answer 21

(see page 52 in the revision guide)

Question 22

Write a full redox equation for magnesium burning in oxygen to produce magnesium oxide and aluminium reacting with chlorine to form aluminium chloride.

Answer 22

(see page 53 in the revision guide)

Question 23

How can a reaction go to completion if few particles have energy greater than the activation energy?

Answer 23

Particles can gain energy through collisions.

Question 24

What happens to the curve of a Maxwell Boltzmann distrbution when temperature is increased?

Answer 24

As the temperature increases the distribution shifts towards having more molecules with higher energies, although the number of molecules with those energies decrease.

The total number of particles remains a constant (the total area under the curve should remain constant.

(shifts to the right and lowers)
(see page 1 in the chemrevise revision guide)

Question 25

What does the Maxwell-Boltzmann energy distribution show?

Answer 25

The Maxwell-Boltzmann energy distribution shows the spread of energies that molecules of gas or liquid have at a particular temperature.

Question 26

Define the rate of reaction.

Answer 26

The rate of reaction is defined as the change in concentration of a substance in unit time. Its usual unit is moldm-3s-1

Question 27

How do you calculate the rate of reaction from a graph of concentration plotted against time.

Answer 27

Draw a tangent.

see page 2 in the chemos revise revision guide

Question 28

What happens to the rate of reaction when you increase the concentrations of reactants?

Answer 28

At higher concentrations there are more particles per unit volume and so the particles collide with a greater frequency and there will be a higher frequency of effective collisions; Therefore a faster rate of reaction.

Question 29

What happens to the rate of reaction when you increase the pressures of reactants?

Answer 29

At higher pressures there are more particles per unit volume and so the particles collide with a greater frequency and there will be a higher frequency of effective collisions; Therefore a faster rate of reaction.

Question 30

What happens to the rate of reaction when you double the concentrations of reactants?

Answer 30

At higher pressures there are double the number of particles per unit volume and so the particles collide with a greater frequency and there will be double the frequency of effective collisions; Therefore a faster rate of reaction.

Question 31

What happens to the shape of a rate of reaction graph when you increase the concentrations of reactants?

Answer 31

The shape of the energy distribution curves do not change (i.e. the peak is still at the same energy) so the Emp and mean energy do not change.

The curve will be higher and the areas under the curve will be greater because there are more particles.

More molecules have energy more than the activation energy, therefore proving that this increases the rate of reaction.

(see page 2 in the chemrevise revision guide)

Question 32

What does Emp stand for?

Answer 32

Emp is the most probable energy (not the same as mean energy)

Question 33

What happens to the rate of reaction when you increase the temperature of reactants?

Answer 33

At higher temperatures the energy of the particles increases. They collide more frequently and more often with energy greater than the activation energy. More collisions result in a faster rate of reaction.

Question 34

What does the rate of reaction graph show when you increase the temperature of reactants?

Answer 34

As the temperature increases, the graph shows that a significantly bigger proportion of particles have energy greater than the activation energy, so the frequency of successful collisions increases.

(see page 3 in the chemrevise revision guide for a graph example)

Question 35

What happens to the rate of reaction when you increase the surface area of reactants?

Answer 35

Increasing the surface area will cause successful collisions to occur more frequently between the reactant particles and this increases the rate of the reaction.

Question 36

Give the definition of a catalyst.

Answer 36

Catalysts increase the rate of reaction without getting used up, they do this by providing an alternative route or mechanism with a lower activation energy.

Question 37

Draw an enthalpy profile diagram for a reaction with and without a catalyst.

Answer 37

(see page 3 in the chemrevise revision guide)

Question 38

How does the use of a catalyst affect the rate of reaction? Explain and draw a Maxwell-Boltzmann distribution curve for with and without a catalyst.

Answer 38

If the activation energy is lower, more particles will have energy more than the activation energy so there will be a higher frequency of effective collisions. The reaction will be faster.