Kinetics

Question 1

What do you say if temperature is increased

Answer 1

MANY more particles have energy greater than or equal to the activation energy

Question 2

Half of the gas molecules in the sample are removed. The remaining gas molecules are kept at the same temperature.

Draw the new distribution of molecular energies for the remaining gas on
the figure above.

Answer 2

M1 Peak should be at same energy (i.e. in line with X)
M1 and M2 marked independently
1
M2 Overall area should be half the original area; after diverging from the
origin, the second line should not touch the first line
M2 area should be about half of the original

Question 3

Suggest, by considering the products of this reaction, why small amounts of reactants are used in this experiment.

Answer 3

as it forms a toxic gas or
SO2 is toxic/poisonous or
to limit amount of SO2 formed

Question 4

Explain, in terms of collision theory, the effect of increasing the
concentration of hydrogen peroxide on the rate of reaction.

Answer 4

M1 more particles/molecules/reactants/H2O2/moles in given/same volume/space
OR
particles/molecules/reactants/H2O2/moles closer together successful collisions are more frequent

(More frequenct successful collisons)

Question 5

Explain why the use of a large excess of H2O2 and I– means that the rate of reaction at a fixed temperature depends only on the concentration of H+ (aq).

They basically zero order

Answer 5

H2O2 and/or I– concentration change is (effectively) constant so have a constant

so is zero order (w.r.t. H2O2 and I–) / a and b are zero

Question 6

On the same axes, draw a curve for sample 1 at a lower temperature.
(2

Answer 6

M1 Curve is higher and displaced to the left
M2 Only crosses the original curve once

Question 7

Explain the effect that lowering the temperature would have on the rate of
reaction.

Answer 7

Fewer particles will have energy greater than or equal to the activation energy
1
Fewer successful collisions in a given time

Question 8

Deduce the change that was made to the reaction conditions.
Explain the effect that this change has on the rate of reaction.

Answer 8

The amount of gas present (or number of molecules) has been reduced /
or the pressure has been reduced
Particles are spread further apart
1
Fewer collisions between gas particles so fewer successful collisions

Question 9

How does temp effect rate

Answer 9

Particles have on average more kinetic energy when they are heated
- A larger proportion of teh molecules will have an energy greater than the activation energy
- a decrease in temo will lead to a smaller propotion of teh molecules having greater than the actibvation energy

Question 10

What effect does increasing and decreasing temp have on the maxwell boltzman distributon curve

Answer 10

Increase in temp:
Curve shifts to the right
Peak is lower
More particles>Ea

Decrease in temp
Curve shifts to the left
Peak is higher
More particles<Ea

The lines should only cross once

Question 11

concentartion AndPressure

Answer 11

Increasing pressure/conc will increase the rate of reaction as partciles are closer toegther and collide more often.
-There are more frequent collisions and a higher chance of a reaction

Question 12

Define rate of reaction

Answer 12

CHnage in conc in unit time

Question 13

Unit for rate

Answer 13

mol dm-3s-1

Question 14

Effect of increasing concentration and increasing pressure

Answer 14

More molecules have energy > EA
(although not a greater proportion)