Effect of Catalysts

Question 1

what are catalysts?

Answer 1

they are substances (usually solids) which:
- increase rate
- remain chemically unchanged

Question 2

how do catalysts work?

Answer 2

catalysts increase rate because:
- they provide an alternative route with a lower activation energy
- so the percentage of collisions with enough energy is higher
- so there are more successful collisions per unit time

Question 3

what is the hydrogen peroxide experiment?

Answer 3

• the effect of a catalyst on rate can be demonstrated using the decomposition of hydrogen peroxide

2H2O2(aq) → 2H2O(l) + O2(g)

Question 4

why are catalysts not in the reaction equation?

Answer 4

they are unchanged during the reaction

Question 5

is the hydrogen peroxide experiment slow or fast?

Answer 5

it is normally very slow, taking days to finish

Question 6

why is the catalyst in the hydrogen peroxide experiment?

Answer 6

• it is catalysed by manganese(IV) oxide, which is a black solid
• this cause it to take place much faster, taking only a few seconds to finish
• you can measure the effectiveness of different catalysts by comparing how they affect rate

Question 7

what are the variables of the hydrogen peroxide experiment?

Answer 7

input = which catalyst is being used
output = volume of oxygen (g)
control:
- volume and concentration of H2O2 (aq)
- temperature
- mass and surface area of catalyst

Question 8

what are the results of the hydrogen peroxide experiment on a graph?

Answer 8

• more effective catalysts increase rate more effectively
• this results in a steeper line on the graph
• the initial amounts of reactants is the same, so all lines would eventually flatten out at the same total volume of oxygen if you waited long enough

Question 9

what is the MnO2 (s) catalysed decomposition of hydrogen peroxide used for?

Answer 9

to produce oxygen in the lab