C6 - The Rate and Extent of Chemical Change

Question 1

What is rate of reaction?

Answer 1

The change in amount of a reactant or product per unit time.

Question 2

What 2 factors does rate depend on?

Answer 2

Frequency of collisions.
Energy of collisions

Question 3

What happens when you increase the temperature of a reaction?

Answer 3

Particles have more kinetic energy, so there are more frequent collisions but also more energetic collisions.

Question 4

What happens to the rate of reaction as the reactant runs out?

Answer 4

As the reactant runs out, the concentration decreases, so the collision frequency is slower, meaning rate of reaction is slower.

Question 5

What is a dynamic equilibrium?

Answer 5

When the rate of the forward and backward reactions are the same, so the net concentration remains constant.

Question 6

What is Le Chatelier’s principle?

Answer 6

If a change is made to the equilibrium, the equilibrium will act to oppose the change.

Question 7

If there are more reactants where does the equilibrium lie?

Answer 7

Left

Question 8

If there are more products where does the equilibrium lie?

Answer 8

Right

Question 9

If the forward reaction is endothermic and the backward reaction is exothermic, and there is an increase in temp. where does the equilibrium lie?

Answer 9

Right - to decrease temp.

Question 10

If the forward reaction is endothermic and the backward reaction is exothermic, and there is an decrease in temp. where does the equilibrium lie?

Answer 10

Left - to increase temp.

Question 11

If there are 4 mol of reactants and 2 mol of products, and there is an increase of pressure where will the equilibrium lie?

Answer 11

Right - to decrease pressure

Question 12

If conc. of reactants is increased, what is the effect on equilibrium?

Answer 12

Right

Question 13

If conc. of products is decreased, what is the effect on equilibrium?

Answer 13

Right

Question 14

How is rate of reaction calculated?

Answer 14

rate of reaction = amount of reactant used or product formed / time

Question 15

State 5 factors affecting the rate of a reaction.

Answer 15

Catalysts
Temperature
Conc. of reactants
Pressure of gases
Surface area

Question 16

What is collision theory?

Answer 16

Chemical reactions can only occur when reacting particles collide with each other with sufficient energy.

Question 17

What is a reversible reaction?

Answer 17

When the products of a reaction can react backwards to produce original reactants.

Question 18

What is activation energy?

Answer 18

The minimum amount of energy particles must collide with for a reaction to happen.

Question 19

What is a catalyst?

Answer 19

A substance that can increase the rate of a reaction while remaining unchanged by the end of the reaction.

Question 20

What do catalysts do to the activation energy of the reaction?

Answer 20

They lower the activation energy by providing an alternative route meaning there is a higher chance that more particles will react.

Question 21

Why are catalysts economical?

Answer 21

They require lower temperatures to start the reaction.

Question 22

How is rate of reaction calculated?

Answer 22

amount of reactant used or product formed / time

Question 23

What are the various units for reaction time?

Answer 23

g/s (mass/time), cm3/s (volume/time), mol/s (moles/time)

Question 24

Name 3 ways of measuring rate of reaction.

Answer 24

Loss in mass of reactants.
Volume of gas produced.
Time for a solution to become opaque.

Question 25

Describe measuring the rate by monitoring mass loss.

Answer 25

Place reaction flask on a balance. In reaction of metal carbonate + acid a gas is given off.
Record decrease of mass in time intervals.

Question 26

Describe measuring the rate by monitoring volume of a gas.

Answer 26

Connect a gas syringe to a reaction flask and measure the volume of a gas formed in time intervals.

Question 27

Describe measuring the rate by monitoring disappearance of a cross.

Answer 27

Put a reaction flask on a piece of paper with a cross on it. Mix the reactants, and measure how long it takes for a cloudy mixture to conceal the cross.

Question 28

5 factors that affect the rate of a reaction.

Answer 28

Concentration of reactants.
Pressure of gases.
Surface area.
Temperature.
Catalysts.

Question 29

What must happen for a reaction to occur?

Answer 29

Particles must collide with at least a minimum amount of energy.

Question 30

How to find rate of reaction from a graph at a certain time?

Answer 30

gradient of tangent

Question 31

How does concentration link to rate of reaction?

Answer 31

Con. increases = faster reaction
More reactants = more frequent collisions

Question 32

How does pressure link to rate of reaction?

Answer 32

Increases number of gas molecules in a given volume.
So, frequency increases so increases rate of reaction.

Question 33

How does surface area link to rate of reaction?

Answer 33

Increase in surface area increases frequency of collisions and so increases rate of reaction.

Question 34

What is an enzyme?

Answer 34

A molecule that acts as a catalyst in a biological system.

Question 35

Describe effect of a catalyst on the position of an equilibium.

Answer 35

No effect.
Forward and backward reactions sped up equally.
However, means equilibrium is achieved quicker.

Question 36

What happens as the reactant runs out in a non-reversible reaction?

Answer 36

Conc. decreases so collision frequency is slower, rate of reaction is slower.

Question 37

How can you increase the surface area of a solid?

Answer 37

Break it down into smaller pieces.