Kinetics

Question 0

What are the 6 factors that affect reaction rate?

Answer 0

Concentration
Pressure
Surface area of a solid
Temperature
Light
Catalyst

Question 1

What is kinetics?

Answer 1

The study of the rate at which a chemical reaction takes place.

Question 2

How does concentration affect Kinetics?

Answer 2

Increasing the concentration of a reactant increases the rate of reaction as there is more likelihood of two reactant molecules colliding and reacting.

Question 3

How does Pressure affect Kinetics?

Answer 3

Increasing the pressure OF A GAS increases the rate of reaction ad the molecules are closer together so are more likely to react.

Question 4

How does the surface area of a solid affect Kinetics?

Answer 4

The larger the surface area the more likely that the particles will co,e into contact with the liquid and react. Finely divided powders react faster than powders with large large particles.

Question 5

How does Temperature affect Kinetics?

Answer 5

As the temperature increases so does the rate of reaction. At a higher temperature the the particles have more energy and move faster and so are more likely to undergo a reaction.

Question 6

Approximately what happens every 10°C rise in temprature?

Answer 6

The reaction rate doubles.

Question 7

How does light affect Kinetics?

Answer 7

The presence of light to provide energy may be necessary for a reaction i.e photosynthesis and the chlorination of methane.

Question 8

What is a catalyst and why are they important?

Answer 8

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

This is important in industry as they can be uses to give a good yield of a product at a lower temperature or pressure. There are also biological catalysts called enzymes.

Question 9

What is the rate of a reaction?

Answer 9

A measure of the chemical change that happens per unit of time?

Question 10

When zinc is added to sulphuric acid they react. The zinc disappears and bubbles of hydrogen are given off. What change could be measured in this reaction to be able to calculate rate?

Answer 10

1. ) The amount of zinc used per minute.
2. ) Amount of sulphuric acid used per minute.
3. ) Amount of zinc sulphate produced per minute.
4. ) Amount of hydrogen produced per minute.

Question 11

How do you calculate the initial rate of a reaction?

Answer 11

At the beginning of the reaction the concentration of all reactants must be known. Plotting the concentration of one of the reactants against time will produce a curve. A tangent to that curve at time zero can be used to calculate the initial rate of reaction.

Question 12

What is collision theory?

Answer 12

This states that for molecules to react they must collide. If they do so at low temperatures the will be moving slowly and might bounce apart again without reacting. At higher temperatures the collisions are more likely to result in bonds being broken and new bonds being made.

Question 13

What is activation energy and what does it act as?

Answer 13

The minimum energy that molecules need to react. This acts as a barrier which molecules have to clear in order to react.

Question 14

What happens as molecules get closer together?

Answer 14

Their potential energy increases and reaches a maximum as the molecules collide and bonds begin to break.

Question 15

Describe the shape of a reaction profile for an exothermic reaction.

Answer 15

Before reaction the energy of the reactants is constant. During the reaction the energy of the reactants goes up to clear the activation energy and then the energy falls to a value lower than that of the initial reactants (as energy is lost as heat.)

Question 16

Describe the shape of a reaction profile for an endothermic reaction.

Answer 16

Before reaction the energy of the reactants is constant. During the reaction the energy of the reactants goes up to clear the activation energy and then the energy falls to a value higher than that of the initial reactants (as energy is absorbed as heat.)

Question 17

Describe the energy states of a collection of the same molecules at a specific temperature and what can this be shown in?

Answer 17

The energy of the molecules will have a spread of values where some have average energy whilst some have below average energy and some have above average energy. This can be shown In an energy distribution curve.

Question 18

What will be shown in an energy distribution curve at low temperatures?

Answer 18

A large number of molecules will have near average energy and a small fraction will have very high or very low energies. So the number of molecules with sufficient energy to react is low.

Question 19

What will be shown in an energy distribution curve at moderate temperatures?

Answer 19

There will be a wider spread of energies and more molecules will have sufficient energy to react.

Question 20

What will be shown in an energy distribution curve at high temperatures?

Answer 20

The number of molecules with moderate and high energies will increase so more molecules wil have sufficient energy to react.

Question 21

How do catalysts work?

Answer 21

They provide an alternate mechanism for the reaction .

Question 22

What are Homogenous catalysts?

Answer 22

This is when the catalysts and reactants are in the same phase. e.g the enzyme actetylcholinesterase which breaks down acetylcholine which is produced in nerve endings when they are stimulated. Once transmitted this substance needs to be broken down very fast to allow the nerve endings to become sensitive again.

Question 23

What are heterogenous catalysts?

Answer 23

If the reaction takes place on the solid surface of the catalyst when the reactants are gasses then this is heterogenous catalysis. Many heterogenous catalysts are transition metals whose D orbitals allow them to bond with many substances to form reactive intermediates. I.e the haver process uses an iron catalyst.

Question 24

What catalyst is used in catalytic converters in cars and how can it be collected?

Answer 24

Palladium. Which could be isolated from waste products of uranium mining using bacteria.