Topic 8 - Rates of Reaction

Question 1

What is the general equation for rate of reaction?

Answer 1

Mean rate of reaction = quantity of reactant used / time or quantity of product formed / time.

Question 1

What are the two ways of finding the rate of reaction?

Answer 1

1. How quickly reactants are used up to make products. 2. How quickly the products are made.

Question 2

What is collision theory?

Answer 2

The idea that particles of reactants need to collide with equal to or more than the activation energy to react.

Question 3

What is activation energy?

Answer 3

The minimum energy required for particles to successfully react during a collision.

Question 4

What is the relationship between material size and surface area to volume ratio?

Answer 4

The smaller the material size, the greater the Surface Area to Volume ratio.

Question 5

What is the relationship between surface area to volume ratio and rate of reaction? Why is this?

Answer 5

The higher the surface area to volume ratio, the faster the rate of reaction. This is due to the particles having a larger surface area to collide with leading to more successful collisions and thus a faster rate.

Question 6

What happens to the rate of reaction when temperature is increased?

Answer 6

1. Particles collide more often due to them having more kinetic energy and thus moving faster. 2. Particles collide with more than the activation energy more often. These two factors increase the rate of successful collisions and thus the rate of reaction.

Question 7

What happens to the rate of reaction when concentration is increased? Why does this happen?

Answer 7

When concentration is increased, rate of reaction increases as there are more particles to collide within the same volume.

Question 8

What happens to the rate of reaction when pressure is increased? Why does this happen?

Answer 8

When pressure is increased, rate of reaction is increased as particles are forced to be closer together within the same volume, meaning collisions are more likely .

Question 9

What is a reactionary catalyst? What happens to it during a reaction and what does it do?

Answer 9

A catalyst increases the rate of reaction by providing a lower activation energy path for the reaction. It is not used up during the reaction.

Question 10

What is a tangent of line?

Answer 10

A line drawn at a point on a curved graph to determine the gradient at that point.

Question 11

What is a reversible reaction?

Answer 11

A reaction where the products and reactants can be returned to their original state. The reaction can happen in two separate directions.

Question 12

What can be said about the energy transfer in a reversible reaction?

Answer 12

One direction is always exothermic and the other direction is always endothermic.

Question 13

What is a closed system?

Answer 13

A system where no new reactants enter and no products leave, the contents of the system are always the same.

Question 14

What is dynamic equilibrium?

Answer 14

Where two sides of a reversible reaction are occurring simultaneously and at the same rate. The reactions are still occurring but their rate being the same makes them in equilibrium.

Question 15

How do you favour the production of C in a reversible reaction A+B <-> C + D where the forward reaction is exothermic and the two reactions are in dynamic equilibrium?

Answer 15

You can decrease temperature in the system so that the exothermic reaction is favoured (which produces C) to counteract the temperature decrease or constantly remove produced C so that it doesn’t react back into C and since the reaction will favour the creation of C if it is not there.

Question 16

What can be said about which side of 2A + B <-> C + D will be favoured if the pressure is increased?

Answer 16

The forward reaction will be favoured to use up the side (2A + B) with more moles to decrease pressure.

Question 17

What is Le Châtelier’s principle?

Answer 17

If a dynamic equilibrium is disturbed by a change in conditions in the closed system, the position of equilibrium (which side of the reaction is favoured) will shift to counteract the movement and re-establish equilibrium.

Question 18

What are the factors that affect rate of reaction?

Answer 18

Temperature, Pressure, Concentration, Surface area to volume ratio and whether catalysts are used.

Question 19

What is the definition of the rate of reaction?

Answer 19

How fast the reaction occurs.

Question 20

When a question asks “until the reaction is complete” on a graph, what does it mean?

Answer 20

It means when the data plateaus and results do not change over time, not when all of the data ends. [C8 Test Review Question]

Question 21

Why are certain metals like Potassium unsuitable to react with acids?

Answer 21

They are very reactive and thus are too dangerous (not to do with groups in questions about rates). [C8 Test Review Question]

Question 22

How do you calculate rate of reaction on a curved graph?

Answer 22

Draw a tangent to the curve at that time.

Construct a right angled triangle using the tangent as the hypotenuse.

Calculate gradient by doing change in y / change in x

Ensure you use units.

Question 23

How do you measure decreasing mass of a reaction mixture to find rate?

Answer 23

Take regular interval recordings of mass, the decrease in mass will be due to the gas given off.

Question 24

How do you measure the volume of gas given off in a reaction?

Answer 24

Use a gas syringe connected to a conical flask to measure volume of gas

Question 25

How do you measure decreasing light passing through a solution?

Answer 25

Some reactions turn a solution cloudy. If you place a piece of paper with an X marked you can time how long it takes to no longer be visible.

Question 26

What factors affecr temperature?

Answer 26

The frequency of collisions.

The amount of energy each particle has during a collision.

Question 27

How do particles exceeding the activation energy affect rate compared with frequency of collisions?

Answer 27

An increased proportion of particles exceeding activation energy has a greater effect on rate than an increased frequency of collisions.

Question 28

How do catalysts work in a reaction?

Answer 28

Catalysts don’t increase the frequency of collisions or make collisions more energetic.

They provide an alternative reaction pathway to the products.

A higher proportion of the reactant particles have sufficient energy to react.

Question 29

What are the advantages of catalysts for the environment?

Answer 29

They mean that you use less fossil fuels as the reaction requires less energy, decreasing the contribution towards the greenhouse effect.

Question 30

What is an example of a reversible reaction?

Answer 30

Hydrated copper(II) sulfate (blue) <–> anhydrous copper (II) sulfate (white) + water

Question 31

What is the reversible reaction for ammonium chloride?

Answer 31

Ammonium Chloride <–> Ammonia + Hydrogen Chloride

Question 32

What is the effect of increasing pressure on a reversible reaction?

Answer 32

As pressure is increased, the side with lower moles output is favoured.

Question 33

What is the effect of increasing the temperature in a reversible reaction?

Answer 33

The endothermic reaction is favoured