C6: The Rate & Extent of Chemical Reactions

Question 1

Any Rate =

Answer 1

change in quantity/time

Question 2

What is an experiment for rate of reaction using a cross?

Answer 2

• Hydrochloric acid + sodium thiosulphte causes solution to go cloudy (higher turbidity)
• Measure time for cross to disappear: repeat at different temperatures

Question 3

What is an experiment for rate of reaction using a gas syringe?

Answer 3

Measure volume of gas produced by attaching gas syringe to reaction vessel

Question 4

What does the graph for rate of reaction look like?

Answer 4

Starts off steeply then plateaus

Question 5

How do you work out gradient from a curve?

Answer 5

Draw a tangent
Gradient = rate of reaction
(unit: g/s or cm3/s)

Question 6

How can the rate of reaction be increased?

Answer 6

-Increase surface area/concentration/pressure. Particles collide more frequently
-Increase temperature: particles move faster, collide more frequently & with more energy; more likely to be successful
-Catalyst reduces activation energy: collisions more likely to be successful

Question 7

What happens in a closed system?

Answer 7

-Both the forward and reverse reaction will continuously take place
-Eventually the rate of both of these will be equal
-EQUILIBRIUM is reached: the overall quantity of both sides will not change

Question 8

What does LE CHATELIER’S PRINCIPLE state?

Answer 8

If a system at equilibrium is subjected to a change, the system will adjust to counteract the change

Question 9

What happens if pressure is increased?

Answer 9

It will favour the reaction that produces fewer moles
The rate of this reaction will increase to produce more ammonia until equilibrium is again reached

Question 10

What happens if product is removed from one side?

Answer 10

Shifts the position of equilibrium in that direction

Question 11

What would an increase in temperature favour?

Answer 11

The ENDOTHERMIC reaction

Question 12

How do you work out the rate at a particular point?

Answer 12

Draw a tangent and work out the gradient

Question 13

What are safety precautions for the disappearing cross practical?

Answer 13

• Constantly wash to avoid contamination
• Don’t go above 60 degrees C because harmful gases will start to be produced
• Don’t get on hands as it will start to irritate

Question 14

What is the practical to measure gas produced?

Answer 14

• Inverted measuring cylinder to collect gas
• Put delivery tube through
• Measure gas in cylinder before starting experiment
• Conical flask with stopper attached to delivery tube
  Add powdered calcium carbonate and gas fills up more quickly

Question 15

What will happen to the rate of reaction when temperature is increased and why?

Answer 15

• The rate of reaction will be faster
• Particles will have more energy
• Can move around faster
• Leading to more successful and frequent collisions

Question 16

What will happen to the rate of reaction when surface area is increased and why?

Answer 16

• The rate of reaction will be faster
• There are more particles available to react
• Leading to more successful collisions

Question 17

What will happen to the rate of reaction when concentration/pressure is increased and why?

Answer 17

• The rate of reaction will be faster
• There are more particles in a fixed volume
• A higher chance of a successful collision

Question 18

What does a catalyst do?

Answer 18

• Lowers the activation energy
• Fixes one of the reactants in place so that it is easier for the other reactant to find it