C5.2

Question 1

What is the rate of a reaction?

Answer 1

Measure of how quickly reactants are used or products are formed
Rate of reaction = mass of reactant used / time
Rate of reaction = mass of product formed / time

Question 2

Why and how do we measure the volume of a gas for rate of reaction?

Answer 2

If the product is in gas state it is easier to measure its volume than mass
- either use an upturned measuring cyclinder in water
OR
Use a gas syringe :
1) place a reactant in a conical flask connected to a gas syringe (make sure it is at 0)
2) add the other reactant and close the flask with a stopper and start the stop clock
3) with a results table, record the tip, e and volume of the gas at regular time intervals

Question 3

How to calculate the mean rate of reaction from a graph?

Answer 3

1) calculate the changes in volume and time over the given time interval
2) calculate the mean gradient = change in volume / change in time

Question 4

What is the collision theory?

Answer 4

Reactions only occur if reactant particles collide with each other and have enough activation energy to react

Question 5

Why would a reaction not occur even with collisions?

Answer 5

Collision didn’t have enough energy OR collision didn’t occur at the correct angle/orientation

Question 6

What are the factors that affect rate of reaction?

Answer 6

• temperature
• concentration
• pressure
• SA
• catalysts

Question 7

How does temperature affect the rate of reaction?

Answer 7

• when you increase the temperature the rate it occurs at increases as particles gain more kinetic energy
• therefore they collide more frequently
• as the particles have more energy a greater proportion would have higher activation energy
• so there are more successful collisions and so a a greater rate of reaction

Question 8

How can you investigate the affect of temperature on rate?

Answer 8

Reaction between sodium thiosulfate solution and hydrochloric acid
1) in a beaker mix the reactants on top of a white tile with a cross and start a stop clock
2) stop the clock when the cross disappears
3) the longer it takes for the cross to disappear the slower the reaction
4) change the temperatures by heating up one of the solutions before reacting them in a water bath of ice bath

Question 9

What is the reaction time and what is its relationship with rate of reaction?

Answer 9

Time taken for reaction to occur
Inversely proportional

Question 10

How does concentration affect rate of reaction?

Answer 10

• When you increase the concentration of a chemical reaction the particles become more crowded than before and so will collide more frequently
• The rate of successful collisions increases and therefore the rate increases

Question 11

How can you investigate the effect of concentration of the rate of reaction?

Answer 11

Reaction between magnesium ribbon and hydrochloric acid
1) measure the time taken for the piece of magnesium ribbon to be used up
2) change the concentrations of hydrochloric by adding water
3) 1/time to find the rate

Question 12

How does pressure of gases affect the rate of reaction?

Answer 12

• with increased pressure of a chemical reaction, the rate of reaction increases
• as the particles become crowded than before (less space)
• collide more frequently in a given time
• therefore a greater rate of reaction

Question 13

How does SA affect rate of reaction?

Answer 13

• with increased SA the surface area to volume ratio increases
• more particles available for collisions
• collisions are more frequent
• rate of successful collisions increases
• greater rate of reaction
  In a solid the particles can only vibrate so only the particles at the surface can react so rate is slower

Question 14

How can you investigate the effect of surface area on rate of reaction?

Answer 14

Reaction between calcium carbonate and dilute hydrochloric acid
1) add dilute hydrochloric acid to a conical flask and stopper it with cotton wiol
2) place the flask on a balance next to a lump of calcium carbonate
3) tare the balance and remove the cotton wool, then drop the calcium carbonate lump into the acid and start a stop clock and put the cotton wool back
4) record the mass at regular intervals as the reading will decrease with CO2 escaping
5) use different forms of calcium carbonate (powder, small chips, large chips)

Question 15

Why are catalysts useful?

Answer 15

Isn’t used up
- only small amounts can be used for a large reaction
- often contain expensive metals

Question 16

How do catalysts work?

Answer 16

Provide an alternate reaction pathway with a lower activation energy
Greater proportion of particles have the required activation energy

Question 17

How can you investigate the effect of a catalyst on the rate of a reaction?

Answer 17

Powdered manganese oxide catalyzes the decomposition of hydrogen peroxide
1) place hydrogen peroxide solution in a conical flask connected to a gas syringe
2) put varying masses of manganese oxide into the flask, stopper it and start the stop clock
3) record the time and volume of oxygen produced at regular time intervals
4) draw a graph to analyse the results