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

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

Answer 3

A

Question 4

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

Answer 4

Tangent

Question 5

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

Answer 5

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

Question 6

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

Answer 6

Activation Energy

Question 7

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

Answer 7

Collision Theory

Question 8

Explain how temperature affects the rate of reaction.

Answer 8

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

Question 9

Explain how surface area affects the rate of reaction.

Answer 9

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

Question 10

Explain how concentration affects the rate of reaction.

Answer 10

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

Question 11

Explain how pressure affects the rate of reaction.

Answer 11

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

Question 12

How does a catalyst work?

Answer 12

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

Question 13

What is a catalyst?

Answer 13

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

Question 14

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

Answer 14

Question 15

What is the symbol for a reversible reaction?

Answer 15

Question 16

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

Answer 16

Exothermic

Question 17

What does ‘equilibrium’ mean?

Answer 17

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