Chemistry (C6)

Question 1

What must happen to the particles of reactants for a chemical reaction to occur?

Answer 1

The particles of the reactants must collide with the correct amount of energy.

Question 2

Do all collisions react in chemical reactions?

Answer 2

No, when particles collide they must collide with enough energy.

Question 3

If a chemical reaction is occurring quickly, then there must be more/less collisions per second?

Answer 3

More.

Question 4

Define activation energy.

Answer 4

Activation energy is the minimum energy needed to start a chemical reaction.

Question 5

Name the 5 ways you could increase the rate of reaction.

Answer 5

Increase in pressure, concentration, surface area or temperature, add a catalyst.

Question 6

Explain how increasing the pressure of a reaction will increase the rate of reaction.

Answer 6

There are the same amount of particles in a smaller volume resulting in more successful collisions per second.

Question 7

Explain how increasing the concentration of a reaction will increase the rate of reaction.

Answer 7

There are more particles in the same volume resulting in more successful collisions per second.

Question 8

Explain how increasing the surface area of a reaction will increase the rate of reaction.

Answer 8

There are more particles exposed resulting in more successful collisions per second.

Question 9

Explain how increasing the temperature of a reaction will increase the rate of reaction.

Answer 9

There are more particles with higher energy or more particles with the activation energy resulting in more successful collisions per second.

Question 10

Define the word ‘catalyst’.

Answer 10

A chemical that increases the rate of a chemical reaction. It is not used up during the reaction and remains chemically unchanged.

Question 11

Explain how adding a catalyst increases the rate of reaction.

Answer 11

Catalysts provide an alternative pathway for particles to collide at a lower energy, lowering the activation energy needed for successful collisions.

Question 12

How do you know the reaction stops on a graph?

Answer 12

Where the graph goes flat/horizontal.

Question 13

Where is the reaction the fastest on a graph?

Answer 13

At the steepest point (the beginning).

Question 14

How can you show the instantaneous rate of reaction on a graph?

Answer 14

Using a tangent.

Question 15

Which of the following units would show a rate of reaction: a. Bpm (beats per minute), b. Metres (m), c. cm3/s, d. g/s?

Answer 15

C and D.

Question 16

Define the word precise.

Answer 16

When measurements are repeated and they are all close to the mean value.

Question 17

Describe an experiment to show how concentration affects the rate of reaction.

Answer 17

Reacting magnesium ribbon with different concentrations of hydrochloric acid. Measure the amount of hydrogen gas produced every 10 seconds up to 100 seconds.

Question 18

Describe the independent, dependent and 2 control variables in the magnesium ribbon experiment.

Answer 18

Independent = concentration of acid. Dependent = volume of gas. Control = same mass of magnesium ribbon, same volume of acid, same person timing, same person collecting the volume of gas.

Question 19

Describe the disappearing cross experiment.

Answer 19

Measure out sodium thiosulfate into a conical flask and dilute with water. Place conical flask on a piece of paper with a black cross on it. Add hydrochloric acid to the flask, swirl gently and start the stop-clock. Stop the clock when you can no longer see the cross. Repeat with different concentration of sodium thiosulphate.

Question 20

What are the independent, dependent and control variables in the disappearing cross experiment?

Answer 20

Independent = concentration of sodium thiosulphate. Dependent = time it takes for cross to disappear. Control = concentration of hydrochloric acid, volume of hydrochloric acid, volume of sodium thiosulphate, same person looking for the cross to disappear each time.

Question 21

True or false: different catalysts work for different reactions.

Answer 21

True.

Question 22

Explain what is meant by a reversible reaction.

Answer 22

A reaction that can go in both directions so the products of a reaction can react together to form the reactants.

Question 23

Describe what is meant by ‘dynamic equilibrium’.

Answer 23

In a reversible reaction an equilibrium is reached when the rate of the forward reaction is equal.

Question 24

Describe Le Chatelier’s principle.

Answer 24

The position of equilibrium will shift to oppose the change introduced.

Question 25

If you increase the temperature of a reaction what will happen to the position of equilibrium?

Answer 25

Equilibrium moves to cool it.

Question 26

If you decrease the pressure of a reaction what will happen to the position of equilibrium?

Answer 26

Equilibrium moves to raise it.

Question 27

Predict which way the position of equilibrium will move if you decrease the temperature.

Answer 27

To the right.

Question 28

Predict which way the position of equilibrium will move if you decrease the pressure.

Answer 28

To the left.

Question 29

Predict which way the position of equilibrium will move if you add a catalyst.

Answer 29

Adding a catalyst has no effect on the position of equilibrium. They increase the rate of reaction for the forward and reverse reaction.

Question 30

Why do we sometimes have to compromise on the position of equilibrium?

Answer 30

A condition might be favoured but the equipment needed is too expensive. Sometimes a lower temperature is favoured but this can slow the rate of reaction so a higher temperature is needed.