Combined Chemistry - C6 The rate and extent of chemical change

Question 1

What two equations can be used to measure the rate of a reaction?

Answer 1

mean rate of reaction = (quantity of reactant used) / time

mean rate of reaction = (quantity of product formed) / time

Question 2

Calculate the mean rate of reaction for the following examples (give the correct unit):

a) A reaction producing 50 cm³ of gas in 5 s.
b) A reaction where 5 g of calcium carbonate completely reacts in 10 s.

*These are just examples, you should be able to calculate rate of reactions for any given reactions.

Answer 2

a) 10 cm³/s
b) 0.5 g/s

Question 3

Higher Q. Calculate the rate of reaction when 2 moles of magnesium oxide reacts in 4 seconds.

*This is just an example, you should be able to calculate rate of reactions for any given reactions.

Answer 3

0.5 mol/s

Question 4

Which reaction shows the fastest rate of reaction? A, B or C?

Answer 4

A

Question 5

What is the name for the straight line drawn next to the curve at the point indicated by the arrow?

Answer 5

Tangent

Question 6

Higher Q. How would you calculate the rate of the reaction at the point indicated by the arrow?

Answer 6

• Draw a tangent at that point
• Calculate the gradient of the tangent

Question 7

List the 5 things that can affect the rate of a reaction.

Answer 7

• Concentration (of solutions)
• Pressure (of gases)
• Surface area (of solids)
• Temperature
• Catalysts

Question 8

What is the name for the minimum amount of energy needed for a reaction to happen?

Answer 8

Activation Energy

Question 9

What theory states that chemical reactions only occur when reacting particles collude with enough energy?

Answer 9

Collision Theory

Question 10

Explain how temperature affects the rate of reaction.

Answer 10

• Increasing temperature…
• …Increases the frequency of collisions…
• …The collisions are more energetic.

Question 11

Explain how surface area affects the rate of reaction.

Answer 11

• Increasing the surface area …
• …increases the frequency of collisions…
• …and so increases the rate of reaction.

Question 12

Explain how concentration affects the rate of reaction.

Answer 12

• Increasing the concentration…
• …increases the frequency of collisions…
• …and so increases the rate of reaction.

Question 13

Explain how pressure affects the rate of reaction.

Answer 13

• Increasing the pressure…
• …increases the frequency of collisions…
• …and so increases the rate of reaction.

Question 14

How does a catalyst work?

Answer 14

• Catalysts increase the rate of reaction…
• …by providing an alternative pathway for the reaction…
• …with a lower activation energy.

Question 15

What is a catalyst?

Answer 15

Something that increases the rate of a reaction without being used up in the reaction.

Question 16

How would you add a line to show the effect of a catalyst on the reaction profile below?

Answer 16

Question 17

What is the symbol for a reversible reaction?

Answer 17

Question 18

If a reversible reaction is endothermic in forward direction, what will it be in the reverse direction?

Answer 18

Exothermic

Question 19

What does ‘equilibrium’ mean?

Answer 19

In a reversible reaction, the forward and reverse reactions occur at exactly the same rate.

Question 20

Higher Q. What is Le Chatelier’s Principle?

Answer 20

The idea that if you change the conditions(such as temperature and pressure) of a reversible reaction at equilibrium, the system will try to counteract the change.

Question 21

Higher Q. What effect will increasing the concentration of a reactant have on a reversible reaction?

Answer 21

• More products will be formed
• Until equilibrium is reached again

Question 22

Higher Q. For a gaseous reaction at equilibrium, what would be the effect of…

a) … increasing pressure
b) … decreasing pressure

Answer 22

a) Equilibrium position will shift towards the side with the smaller number of molecules
b) Equilibrium position will shift towards the side with the larger number of molecules

Question 23

Higher Q. For a reversible reaction at equilibrium, what effect will increasing temperature have on…

a) … the endothermic reaction
b) … the exothermic reaction

Answer 23

a) Endothermic reaction: The amount of product increases
b) Exothermic reaction: The amount of product decreases

Question 24

Higher Q. For a reversible reaction at equilibrium, what effect will decreasing temperature have on…

a) … the endothermic reaction
b) … the exothermic reaction

Answer 24

a) Endothermic reaction: The amount of product decreases
b) Exothermic reaction: The amount of product increases