9: Kinetics I

Question 1

What do particles need to react?

Answer 1

Minimum (activation) energy

Correct orientation relative to each other

Question 2

What is an example of particles needing the correct orientation?

Answer 2

Bromoethane will only react with hydroxide ions if the hydroxide ion collides with the carbon bonded to the bromine

Question 3

What happens when particles collide with less than activation energy?

Answer 3

No reaction

Will bounce off each other

Question 4

What is the activation energy?

Answer 4

Minimum energy required before a reaction can occur

Question 5

What does bond breaking and forming do?

Answer 5

Bond breaking - requires input of energy

Bond forming - releases energy

Question 6

What is the equation for reaction rate?

Answer 6

Change in concentration / change in time

Gradient of tangent in a concentration vs time graph

Question 7

How can the initial rate of reaction be calculated?

Answer 7

Gradient of tangent drawn at time = 0

Question 8

What can increase the rate of a reaction?

Answer 8

Increase temperature
Increase concentration of reactants
Increase SA of solids
Increase pressure of gases
Addition of catalysts

Question 9

How does increasing temperature increase the rate of reaction?

Answer 9

Particles have more kinetic energy on average
Collide more energetically
Greater proportions of particles collide with greater than activation energy

Question 10

How does increasing concentration of reactants increase the rate of reaction?

Answer 10

Greater number of particles per unit volume

More collisions & successful ones per second

Question 11

How does increasing surface area of solids increase the rate of reaction?

Answer 11

Greater number of particles exposed
Reactants collide more frequently
More collisions per second

Question 12

How does increasing pressure of gases increase the rate of reaction?

Answer 12

Same number of gas particles in a smaller volume

More collisions & successful ones per second

Question 13

How does adding a catalyst increase the rate of reaction?

Answer 13

Provides alternative pathway for reaction
Has lower activation energy
More collisions have more than activation energy

Question 14

What occurs to a catalyst during the reaction?

Answer 14

It is not used up

Question 15

What should be said when talking about rates of reaction?

Answer 15

State relative amounts - per unit volume, per second etc.

Question 16

What is a Maxwell-Boltzman curve?

Answer 16

Distribution of energy among particles
x - energy
y - number of particles with that energy

Question 17

What is temperature?

Answer 17

Average kinetic energy of its particles

Question 18

What is the dotted line in the Maxwell-Boltzman curve?

Answer 18

Activation energy - particles with energy right of the line can collide successfully

Question 19

Why does the Maxwell-Boltzman curve start at (0,0)

Answer 19

No particles with no energy

Question 20

What are some notable features of the Maxwell-Boltzman curve?

Answer 20

Distribution doesn’t fall to 0 at highest energies
Area under curve proportional to number of gas particles present
Only particles right of dotted line will react when they react

Question 21

How does the Maxwell-Boltzman curve change when the temperature increases?

Answer 21

Peak is lower and to the right of original peak
Area under curve should be the same
More particles with energy over activation energy

Question 22

What are the two temperatures called in the Maxwell-Boltzman curve?

Answer 22

T1 - original temperature

T2 - higher/new temperature

Question 23

How does using a catalyst change the Maxwell-Boltzman curve?

Answer 23

Shifts the activation energy to the left

More particles have energy above it

Question 24

How does a catalyst change an energy-profile diagram?

Answer 24

Reduces height of the activation energy

Question 25

How can rate of reaction be measured?

Answer 25

Monitoring loss of mass | Monitoring production of gas

Question 26

What is a phase?

Answer 26

Phase is a physically distinctive form of matter | Liquid, solid, gas

Question 27

What are the two types of catalysts?

Answer 27

Heterogeneous | Homogeneous

Question 28

What is a heterogeneous catalyst?

Answer 28

Catalyst is in a different phase from the reactants | Usually solid catalyst with liquid/gas reactants

Question 29

What is a homogeneous catalyst?

Answer 29

Catalyst is in the same phase as the reactants

Question 30

How does a solid heterogeneous catalyst work?

Answer 30

Selectively causes one reactant to bond to but not react with it (adsorb) Weakens the bonds making it more reactive Products deadsorb and are released

Question 31

Why is using an expensive catalyst still economically viable?

Answer 31

Product is produced at a faster rate More money made by the company per (week/month/year) Overall this causes an increase in profit

Question 32

How is pressure related to concentration?

Answer 32

pV = nRT p = (n/V) * RT Therefore pressure is directly proportional to concentration

Question 33

What does a heterogeneous catalyst do to the reaction profile?

Answer 33

Singular smaller peak | Therefore smaller activation energy

Question 34

How does a homogeneous catalyst work?

Answer 34

Reactants combine with catalyst to make an intermediate | Intermediate then reacts to form products and reforms catalyst

Question 35

What does a homogeneous catalyst do to the reaction profile?

Answer 35

First small peak (smaller than without) to form intermediate | Then even smaller peak after this

Question 36

Why is there less energy when reacting with an intermediate species?

Answer 36

Intermediates are highly reactive and unstable so little energy required for them to react

Question 37

Why are catalysts used?

Answer 37

Economic benefits in the long-term | Can change the properties and make a more useful product