Topic 6 - Rate of reaction

Question 1

What are the ways we can calculate the mean rate of reaction?

Answer 1

Question 2

What are the two ways to measure rate of reaction?

Answer 2

Change in mass - We can use this if a gas is produced as the mass will decrease.
Volume of gas produced - We measure the volume of a gas produced

Question 3

What is the method to measure rate of reaction in change in mass?

Answer 3

1) The reaction mixture is placed on a balance.
2) As the reaction takes place, if a gas is produced the mass will decrease.
3) The mass of the mixture recorded at regular time intervals.
4) The rate of reaction can be determined using
Rate = change in mass/change in time
Units are g/s

Question 4

What is the method to measure rate of reaction in change in volume of gas produced?

Answer 4

1) The reaction cylinder is either connected to a gas syringe.
2) As the reaction takes place, if a gas is produced the apparatus will collect the gas.
3) The volume of the gas produced is recorded at regular time intervals.
4) The rate of reaction can then be determined using Rate = volume of gas produced / Change in time.
Units are in cm³/s

Question 5

How can we calculate the rate of reaction between two points in a time on a graphs?

Answer 5

1) Use graph to find the amount of substance at each time.
2) Find the change in the amount.
3) Find the change in time.
4) The mean rate between the two times is given by
mean rate = change in the amount / change in time.

Question 6

How can we calculate the mean rate of reaction at a specific time on a graph?

Answer 6

1) Draw a tangent to the curve at the specific time required.
2) Find the gradient of the tangent.
3) The gradient is the mean rate.

Question 7

What are the 5 main factors that affect rate of reaction?

Answer 7

Temperature
Pressure
Concentration
Surface area
Catalysts

Question 8

Define activation energy?

Answer 8

The minimum amount of energy needed for a reaction to take place.

Question 9

What does the collision theory state?

Answer 9

That chemical reactions can only occur when reactant particles collide with each other and have sufficient energy.

Question 10

What happens to the rate of reaction if we increase the temperature and why?

Answer 10

The particles have more kinetic energy. So they move more quickly. So there are more frequent collisions. So there are higher number of successful collisions. So the rate of reaction increase.

Question 11

What happens to the rate of reaction if we increase the pressure and why?

Answer 11

The particles are more crowded in a smaller area.
There are more frequent collisions.
The rate of reaction increases.

Question 12

What happens to the rate of reaction if we increase the concentration and why?

Answer 12

The particles are more crowded.
There are more frequent collisions.
The rate of reaction increases.

Question 13

What happens to the rate of reaction if we increase the surface area and why?

Answer 13

Increasing the surface area increases the number of reactant particles exposed.
There are more frequent collisions.
The rate of reaction increases.

Question 14

What happens to the rate of reaction if we increase the catalysts and why?

Answer 14

Catalysts speed up the rate of reaction without being used up.
Catalysts provide an alternative reaction pathway with a lower activation energy.
This means a greater proportion of particles will have energy exceeding the activation energy when they collide.
This means there will be more successful collisions and the rate of reaction increases.

Question 15

Define a reversible reaction. ⇌

Answer 15

Is one where the products can react to form the original reactants.

Question 16

How do you change the direction of some reversible reactions?

Answer 16

Changing the conditions. For example, temperature.

Question 17

If a reversible reaction is endothermic in one direction what is it in the other direction?

Answer 17

It will be exothermic in the opposite direction.
Equal amount of energy will be transferred in each direction.

Question 18

In this reaction what reaction is the forwards and backwards reaction? And what happens?

Answer 18

When heated water is removed from the blue hydrated copper sulfate, leaving the white anhydrous copper sulfate.
Colour changes from blue to white when heated.

Question 19

Define equilibrium.

Answer 19

A reversible reaction where the forwards and backwards reactions both happen at the same rate. (Must be in a closed systems, no reactants and products can escape.)

Question 20

What does the position of equilibrium be controlled by?

Answer 20

Changing the concentration.
Changing the temperature.
Changing the pressure.

Question 21

Why is changing the position of equilibrium useful industrially?

Answer 21

We can make more products so the process will be more profitable. If we can shift the equilibrium to the position of the product we desire. Makes process more profitable.

Question 22

What reaction profile is this?

Answer 22

Exothermic

Question 22

What reaction profile is this?

Answer 22

Endothermic

Question 23

What is Le Chatelier’s principle?

Answer 23

If a system at equilibrium is subjected to change the system will adjust to counteract the change.

Question 24

What effect does increasing the concentration have on the equilbrium?

Answer 24

If we increase concentration of a substance the equilibrium shifts to the opposite side of the substance.

Question 25

What happens if we increase the concentration of nitrogen?

Answer 25

The equilibrium shifts to the right. So more NH₃ is made.

Question 26

What effect does increasing the temperature have on the position of equilibrium?

Answer 26

Shifts to the side based on if the reaction is exothermic or endothermic. If increase in temperature will shift to the endothermic side.

Question 27

What is the word and symbol equation for the haber process and what is the forward and backwards reaction?

Answer 27

Word equation - nitrogen + hydrogen → ammonia Balanced symbol equation - N₂(g) + 3H₂(g) ⇌ 2NH₃(g). Forward reaction = Exothermic Backwards reaction = endothermic.

Question 28

What happens to the position of equilibrium if we increase the temperature in the haber process?

Answer 28

Forward reaction = exothermic The equilibrium will shift to the the the endothermic direction so less ammonia made.

Question 29

What happens to the equilibrium if we increase the pressure?

Answer 29

The equilibrium shifts to the side with fewer moles.