Kinetics 1

Question 1

What is collision theory

Answer 1

Collision theory states that for a reaction to take place, between two particles, they must collide with enough energy to break bonds. The collision must also occur between the two parts of the molecule that are going to react together, so orientation has a part to play.

Question 2

What are the five factors that increase the rate of chemical reactions

Answer 2

1) Increasing the temperature
2) Increasing the concentration of a solution
3) Increasing the pressure of a gas reaction
4) Increasing the surface area of solid reactants
5) Using a catalyst

Question 3

Explain why increasing temperature increases the rate of a chemical reaction

Answer 3

• Increasing temperature gives the particles more kinetic energy.
• This means that the collision frequency increases, so the number of successful collisions increases.
• It also means that the particles collide with more energy which means that a higher percentage of the particles collide with the activation energy and so there are more successful collisions.

Question 4

Explain why increasing the concentration of a solution increases the rate of a chemical reaction

Answer 4

• Increasing concentration increases the number of particles per unit volume and this means that the collision frequency increases.
• The more collisions there are, the greater the number of successful collisions.
• However as a reaction proceeds, the reactants are used up and so their concentration falls- in most reactions the rate of reaction drops as the reaction goes on.

Question 5

Explain why increasing the pressure of a gas reaction increases the rate of reaction

Answer 5

• Increasing pressure increases the number of gas particles per unit volume.
• This increases the frequency of collisions
• Higher collision frequency means more successful collisions.

Question 6

Explain why increasing the surface area of solid reactants increases the rate of reaction

Answer 6

• The greater the total surface area of a solid, the more of its particles are available to collide with molecules in a gas or liquid.
• There are more sites for the reaction.
• This increases the frequency of collisions between the solid and other reactants.
• More collisions results in a higher number of successful collisions.

Question 7

Explain why using a catalyst increases the rate of reaction

Answer 7

A catalyst increases the rate of reaction by creating an alternative reaction pathway with a lower activation energy. The catalyst is not used up by the reaction so can be reused repeatedly.

Question 8

What is the activation energy

Answer 8

The minimum amount of energy required for a reaction to occur. It has the abbreviation Ea

Question 9

What is a transition state/activated complex

Answer 9

• The species that exists on top of the curve on an enthalpy diagram is called a transition state/activated complex.
• Some bonds are in the process of being made and some are in the process of being broken.
• It has extra energy and is unstable.

Question 10

What is a Maxwell-Boltzmann distribution curve

Answer 10

The shape of the graph when you plot Energy E against fraction of particles with Energy E

Question 11

What does a Maxwell-Boltzmann distribution curve show us about the distribution of energy among particles

Answer 11

• no particles have zero energy
• most particles have intermediate energies- around the peak of the curve
• A few particles have very high energies: the right hand side of the curve. There is no upper limit.
• The average energy isn’t the same as the most probable energy.

Question 12

How do we use Maxwell-Boltzmann curves and activation energy together

Answer 12

If you mark the activation energy on a Maxwell-Boltzmann graph, then the area under the graph to the right of the activation energy line represents the number of particles with enough energy to react.

Question 13

Describe how temperature affects Maxwell-Boltzmann distribution curves

Answer 13

• At higher temperatures, the peak of the curve is lower and it moves to the right.
• The number of particles with very high energy increases.
• The total area under the curve is the same for each temperature because it represents the same number of particles.
• As there are more particles with higher energy, the graph shows us that more particles have the activation energy.

Question 14

How do catalysts work

Answer 14

• Catalysts increase the rate of a reaction by creating an alternative reaction pathway with a lower activation energy.
• They are not used up by the reaction/remain unchanged at the end.

Question 15

What do catalysts affect and what don’t they affect

Answer 15

• Catalysts lower the activation energy of a reaction
• Catalysts do not affect the enthalpy change of a reaction, nor do they affect the position of equilibrium in a reversible reaction.

Question 16

What catalyst is used for the Haber process and why is it useful

Answer 16

Iron.
The Haber process forms ammonia which is used when making fertilisers.

Question 17

What catalyst is used for the Otswald process and why is it useful

Answer 17

Platinum and rhodium.
The Otswald process produces nitric acid which is useful for making fertilisers and explosives.

Question 18

What catalyst is used for the hardening of fats with hydrogen and why is it useful

Answer 18

Nickel.
This process is useful for making margarine.

Question 19

What catalyst is used to crack hydrocarbon chains from crude oil and why is it useful

Answer 19

-Zeolite catalyst
- Aluminium dioxide and silicon dioxide
- cracking is useful for making petrol

Question 20

What catalyst is used in the catalytic converter in car exhausts and why is it useful

Answer 20

Platinum,palladium and rhodium.
This is useful as catalytic converters stop polluting gases entering the atmosphere.

Question 21

What catalyst is used in the hydration of ethene to produce ethanol and why is it useful

Answer 21

• H+ absorbed on solid silica phosphoric acid, H3PO4
• it is useful as it makes ethanol which is a fuel,additive, solvent and chemical feedstock.

Question 22

What catalyst is used for esterification and why is it useful

Answer 22

• H+
• esterification is useful for making solvents

Question 23

Describe the structure of a catalyst in a catalytic converter

Answer 23

• The catalytic converter is a honeycomb, made of a ceramic material coated with platinum and rhodium metals (the catalysts)
• The honeycomb shape provides a large surface area, on which the reactions take place so a little of the expensive metals goes a long way.

Question 24

What are two of the main reactions that take place in catalytic converters

Answer 24

1) carbon monoxide + nitrogen oxides —> nitrogen + carbon dioxide
2) hydrocarbons + nitrogen oxides —> nitrogen + carbon dioxide + water

Question 25

In what two steps do the reactions with catalysts (in catalytic converters) take place

Answer 25

1) Adsorption
2) desorption

Question 26

Describe how the reactions on the surface of catalysts (in catalytic converters) take place

Answer 26

1) The gases first form weak bonds with the metal atoms of the catalyst- this process is called adsorption. This holds the gases in just the right position for them to react together. The gases then react on the surface.
2) The products then break away from the metal atoms- this process is called desorption. This frees up room on the catalyst surface for more gases to take their place and react.