C6 - The Rate and Extent of Chemical Change

Question 1

What does ‘rate of chemical reactions’ mean?

Answer 1

Speed at which reactants get turned into products

Question 2

Examples of reactions:

Answer 2

• Rusting of iron
• Reaction between a metal and an acid
• Explosions like fireworks

Question 3

How do you the calculate rate of reaction? (1)

Answer 3

Quantitation of Reactants used (g or cm3)
÷
Time Taken

Question 4

How do you the calculate rate of reaction? (2)

Answer 4

Quantity of Products formed (g or cm3)
÷
Time Taken

Question 5

How does the rate of reaction change throughout the process?

Answer 5

The rate is fast at the beginning of the reaction but will slow down as the reaction progresses.

Question 6

What factors affect the rate of chemical reactions?

Answer 6

1. Temperature
2. Surface area
3. Pressure/Concentration
4. Catalyst

Question 7

What is collision theory?
How does this link to rate of reactions?

Answer 7

• For particles to react with each other they have to collide with sufficient amount of energy (activation energy)
• So the rate of reaction will rely on how much energy particles have and frequency of collisions so there is more successful collisions.
• This means to increase rate you have to increase collision frequency or increase particle energy.

Question 8

How does temperature affect rate of reaction?

Answer 8

1. Temp increases
2. Particles have more kinetic energy
3. Particles move faster
4. Particles collide more frequently
5. Collide with more energy
6. More successful collisions
7. Increase rate of reaction

Question 9

How does concentration/pressure affect rate of reaction? (Particles per unit of volume)

Answer 9

1. Either are increased
2. More particles per unit of volume
3. More frequent collisions
4. More successful collisions
5. Increase rate of reaction

Question 10

How does surface area affect rate of reaction?

Answer 10

1. Higher surface area
2. More area for particles to collide
3. More frequent collisions
4. More successful collisions
5. Increase rate of reaction

Question 11

How does the presence of a catalyst affect rate of reaction?

Answer 11

1. Catalyst lowers activation energy
2. Provides an alternative reaction pathway
3. Higher proportion of successful collisions
4. Increased rate of reaction

Question 12

How do you find the actual rate of reaction at a particular time on a graph?

Answer 12

1. Draw tangent to point
2. Find gradient of tangent using change in y/change in x
3. Use formula to find answer using the values you have

Question 13

What do reversible reactions look like? What do they mean?

Answer 13

• Symbol: ⇌
• Forward reaction: top arrow shows reactants can break down/combine into products
• Backward reaction: bottom arrow shows products can break down/combine into reactants

Question 14

What is equilibrium?

Answer 14

• Forward reaction and backwards reaction occur at same speed
• Concentration of reactants and products won’t change anymore
• Both reactions are still happening but they just cancel each other out

Question 15

When can equilibrium only be reached? What does this mean?

Answer 15

• In a closed system
• This is a sealed environment where no reactants or products can escape

Question 16

What does ‘Le Chatelier’s Principle’ say?

Answer 16

• If you change the conditions of a reversible reaction
• position of equilibrium will shift
• to counteract the change

Question 17

How does temperature affect the position of equilibrium?

Answer 17

1. Add heat
2. Favours whichever reaction is endothermic
3. Equilibrium moves to this side

Question 18

How does pressure affect the position of equilibrium?

Answer 18

1. Increase pressure
2. Equilibrium will move to whichever side brings the pressure back down
3. So equilibrium moves to side with less molecules (whichever side of equation has less moles)

Question 19

How does concentration affect the position of equilibrium?

Answer 19

1. If concentration of one side is increased
2. Equilibrium will shift to other side which is less concentrated