Kinetics I

Question 1

In order for a reaction to take place it must have

Answer 1

“the right conditions
Collide in the correct orientation

Collide with sufficient energy know as Ea”

Question 2

In terms of collision theory, describe the effect in an increase of concentration

Answer 2

At higher concentrations there are more particles per unit volume and so the particles collide with a greater frequency and there will be a higher frequency of successful collisions.

Question 3

In terms of collision theory, describe the effect of an increase in temperature

Answer 3

At higher temperatures the kinetic energy of the particles increases. They collide more frequently and more often with energy greater than the activation energy. More collisions result in a reaction

Question 4

In terms of collision theory, describe the effect in an increase in pressure

Answer 4

At higher pressures there are more gas molecules per unit volume and so the particles collide with a greater frequency and there will be a higher frequency of successful collisions.

Question 5

In terms of collision theory, describe the effect in an increase in surface area

Answer 5

Increasing surface area will cause successful collisions to occur more frequently between the reactant particles and this increases the rate of the reaction.

Question 6

How do we calculate the ROR from data showing the time taken from a reaction?

Answer 6

rate of reaction =

Δ[reactants or products] / Δ time mol dm-3s-1)

Question 7

How do we calculate the ROR from the gradient of a graph ?

Answer 7

draw a tangent at the point specified and use Change in y over change in x

Question 8

What is the Maxwell Boltzmann Distribution?

Answer 8

The Maxwell-Boltzmann energy distribution shows the spread of energies that molecules of a gas or liquid have at a particular temperature

Question 9

How can a reaction go to completion if few particles have energy greater than EA?

Answer 9

Particles can gain energy through collisions

Question 10

In a MBD the area under the graph represents

Answer 10

the total number of particles present

Question 11

Where can’t we look at when searching for the mean energy in a MBD graph?

Answer 11

“Not the peak of the curve

The mean energy of the particles”

Question 12

On a MBD would the energy distribution go through the origin?

Answer 12

The energy distribution should go through the origin because there are no molecules with no energy

Question 13

What does the peak in the MBD represent?

Answer 13

Emp this is the most probable energy (not the same as mean energy)

Question 14

In a MBD, are there lots of particles with energy greater than the Ea?

Answer 14

No only a few particles have energy greater than the EA

Question 15

In terms of MBD, how does change in temperatures affect ROR.

Answer 15

As the temperature increases, the graph shows that a significantly bigger proportion of particles have energy greater than the activation energy, so the frequency of successful collisions increases vice versa

Question 16

What is the role of a catalyst?

Answer 16

“Catalysts increase reaction rates without getting used up.

They do this by providing an alternative route or mechanism with a lower activation energy”

Question 17

Describe the action of a catalyst in terms of MBD

Answer 17

If the activation energy is lower, more particles will have energy > EA, so there will be a higher frequency of effective collisions. The reaction will be faster

Question 18

Define homogeneous reactions

Answer 18

is one that takes place in a single phase

Question 19

Define heterogeneous reactions

Answer 19

is on me which the reactants are in two phases

Question 20

The use of a solid catalyst for industrial reactions in the gas phase

Answer 20

The surface area of a solid in a heterogenous reaction is increased (by decreasing the particle size) there’ll be more surface for the reactants to react. This causes more frequent successful collisions increasing ROR.

Question 21

What are the economic benefits of the use of a catalyst in industrial reactions?

Answer 21

they allow the reactions to process at a fast rate at a much lower temperature. This reduces the costs energy since there’ll be less heat heat lost at lower temperature temperature Because the reaction is faster, more products will be produced in a shorter time. This increases efficiency and costs of the process

Question 22

Define the term activation energy

Answer 22

The minimum amount of energy which particles need to collide to start a reaction.