P1: Kinetics

Question 1

Explain the 3 key points of ‘collision theory’

Answer 1

1. For a reaction to take place between two particles, they must collide with enough energy to break bonds, and be in the correct orientation
2. To get a lot of collisions, you must have a lot of particles in a small volume, and must be moving fast to break the bonds.
3. Most collisions between molecules or other particles do not lead to a reaction.

Question 2

What are the 5 factors affecting rate of reaction and explain them?

Answer 2

• INCREASING TEMPERATURE: increases both energy and number of collisions, due to a speed increase.
• INCREASE IN CONC OF SOLUTION: more particles are present, so collisions are more likely, reaction is faster. ( same for an ^ pressure in gas).
• INCREASE SURFACE AREA: more particles are available to collide e.g cube vs granulated sugar
• CATALYST: lowers the activation energy without being used up itself, speeds it up, increases proportion of successful collisions.

These increase the frequency of collisions

Question 3

Define activation energy (Ea)

Answer 3

The minimum energy required for a reaction to occur.

Question 4

What does the ‘Maxwell Boltzmann Distribution’ tell us?

Answer 4

The distribution of energy amongst the particles

Question 5

What are some key points to note about the ‘Maxwell Boltzmann Distribution’?

Answer 5

• No particles have zero energy
• Most particles have intermediate energy (around the peak of the curve)
• A few have very high energies, there is no upper limit
• Average energy is not the same as the most probable energy.

Question 6

How would you work out the total number of particles using the ‘Maxwell Boltzmann Distribution’?

Answer 6

Work out the area under the graph

Question 7

What happens to the ‘Maxwell Boltzmann Distribution’ if we increase the temperature?

Answer 7

-The curve will get lower as there are more particles with greater energy
-Also a higher number of particles with greater energy than the activation energy.
-Will skew slightly more to the right of the original curve.
-area under the curve is the same.

Question 8

Define what a Catalyst is

Answer 8

They provide a quicker alternate pathway or route for the reaction, one with a lower activation energy, and doesn’t get used up or changed itself.

Question 9

What catalyst is used in The Haber Process and what is the reaction?

Answer 9

Iron

N2 (g). +. 3H2 (g). &raquo_space; 2NH3 (g)

Question 10

What catalyst is used to harden fats with hydrogen and what is the reaction?

Answer 10

Nickel

H2C=CH2 + H2&raquo_space;> CH3CH3

Question 11

What are the catalysts in a catalytic converter in car exhausts?

Answer 11

Platinum and Rhodium

Question 12

What catalysts are used to crack hydrocarbon chains from crude oil?

Answer 12

Zeolite, aluminium oxide, and silicon dioxide.

Question 13

What does a catalytic converter do?

Answer 13

Reduces the number of polluting gases coming out of petrol-engine car exhausts.

Question 14

What is the structure of a catalytic converter?

Answer 14

-A honeycomb ceramic material, coated with platinum and rhodium metals.
-Honeycomb shape provides a large surface area.

Question 15

What is the word equation for a catalytic converter?

Answer 15

Carbon monoxide + nitrogen oxides&raquo_space;> nitrogen + carbon dioxide

Question 16

What is Adsorption?

Answer 16

1st reaction that takes place on the surface of the catalyst.

-The gases first form weak bonds with the metal atoms of the catalyst: this holds the gases loosely, to react together.

Question 17

What is Desorption?

Answer 17

2nd reaction to take place on the surface of the catalyst.

-Products break away from metal atoms, freeing up room on the catalyst surface for more gases to take their place and react.

Question 18

Define rate of reaction

Answer 18

Measurement of change in concentration or amount of products or reactants in unit time.

Question 19

What is a transition state?

Answer 19

The top of the curve in and energy level diagram, bonds are being broken and made.

Question 20

Discuss an exothermic reaction with regards to activation energy.

Answer 20

A large activation energy means a slower reaction.

Smaller activation energy means faster reaction as it requires less energy to get going.

Question 21

Talk about endothermic energy

Answer 21

Products have more energy than reactants.

Question 22

Why don’t most collisions between gas-phase reactants not lead to a reaction?

Answer 22

The molecules do not have enough energy (sufficient).

Question 23

Why does a small increase in temp lead to a large increase in rate of reaction between colliding particles?

Answer 23

MANY more particles will have energy greater than the activation energy, so more successful collisions.

Question 24

Explain how a catalyst works

Answer 24

Creates an alternate route for reaction, lowering the activation energy= faster rate of reaction.

Question 25

How do you work out rate?

Answer 25

Rate= 1/ time

Question 26

What is a Heterogeneous catalyst?

Answer 26

Where the catalyst is in a different state/phase to the reactants. e.g reactant: aq catalyst: solid

Question 27

What is a Homogeneous catalyst?

Answer 27

Where the catalyst is in the same state/phase as the reactants. e.g reactant: aq catalyst: aq

Question 28

How do catalysts speed up reactions? (Homogeneous)

Answer 28

They lower the activation energy, so more particles can react as the have sufficient energy, therefore a faster reaction. They create an intermediate.

Question 29

How do Heterogeneous catalysts work?

Answer 29

The reaction occurs on the surface of the catalyst through adsorption, binds to active site, then desorption.

Question 30

If two molecules collide but don’t have enough energy to react, what happens?

Answer 30

They will bounce off each other, and one may gain kinetic energy from the other

Question 31

Where is the highest point of energy in a reaction profile?

Answer 31

The transition state (the peak)

Question 32

What happen to the Maxwell Boltzmann Distribution if you decrease the temperature?

Answer 32

-The peak skews to the left of the original curve -The peak is higher -The activation energy is lower

Question 33

What are the labels on the X and Y axis of a reaction profile?

Answer 33

X= Progress of reaction Y= Energy

Question 34

What are the X and Y axis of a Maxwell Boltzmann Distribution ?

Answer 34

X= Energy Y= Number of particles/molecules

Question 35

Where should the most probable energy, and average energy be on a Maxwell Boltzmann Distribution?

Answer 35

Most probable: The centre of the peak Average: Just to the right of the most probable

Question 36

What 2 factors increase the proportion of successful collisions, therefore increasing rate of reaction?

Answer 36

Kinetic energy: the faster they move the more successful collisions as they have enough energy to break bonds Orientation: some may repel each other and will not collide

Question 37

Briefly describe the required practical for rate of reaction

Answer 37

-Place 10cm3 of 0.05 mol/dm-3 of sodium thiosulfate into a test tube and place over the cross in water -note the starting temperature -add 1cm3 of hydrochloric acid and start timing -stop timer when you can no longer see the cross and record temp -take an average of the time -repeat with different temps -plot on graph