Kinetics 3.1.5 (AS)

Question 1

what is the rate of reaction defined as

Answer 1

The change in concentration of a substance in unit time.

Question 2

what is the equation to work out rate

Answer 2

rate = amount of reactant used or product made / time

Question 3

What is collision theory

Answer 3

• reactions can only occur if the particles collide in the correct orientation
• they must also have minimum energy to collide known as the activation energy

Question 4

what is the activation energy

Answer 4

the minimum energy which particles need to collide to start a reaction

Question 5

what does the maxwell-boltzmann distribution show us

Answer 5

the energy in gas particles

Question 6

why must the maxwell boltzmann graph start at the origin

Answer 6

No particles have zero kinetic energy

Question 7

what’s on the y and x axis of the maxwell boltzmann graph

Answer 7

y axis : number of molecules
x axis : kinetic energy

Question 8

what does the area under the curve of a maxwell boltzmann distribution represent

Answer 8

the total number of particles present

Question 9

what does the peak of the maxwell boltzmann distribution curve represent

Answer 9

The most likely energy of a particle in a sample ( Emp) ( the mode)

Question 10

what does the point on the right of the peak represent in a maxwell boltzmann distribution curve

Answer 10

the mean energy of the particles

Question 11

where is the activation energy in a maxwell distribution curve

Answer 11

near the bottom , where it starts to plateau

Question 12

what does the area under the activation energy of a maxwell boltzmann distribution mean

Answer 12

particles with energy greater than the activation energy can react
- only a few particles have energy greater than the Ea

Question 13

why should the energy distribution of a maxwell boltzmann curve never meet the x axis

Answer 13

there is no maximum energy for molecules

Question 14

where in a maxwell boltzmann curve do particles have low energy and why

Answer 14

Before reacting the Emp ( peak of the curve )
- Because collisions cause some particles to slow down

Question 15

where in a maxwell boltzmann distribution curve do most particles move with moderate speeds

Answer 15

in between the emp and the mean energy

Question 16

what would the maxwell boltzmann curve look like if you increase temperature

Answer 16

• the total area under the curve should remain constant because the total number of particles is constant
• lower peak
• wider
• Area under the Ea is higher
• curve shifts to the right

Question 17

what would the maxwell boltzmann curve look like if temperature decreases

Answer 17

• curve shifts to the left
• peak is higher
• area under curve is the same
• area under curve beyond activation energy decreases

Question 18

why do we get a faster rate of reaction when temperature is increased

Answer 18

They collide more frequently and more often with energy greater than the activation energy .
This results in more frequency of successful collisions

Question 19

How do concentration and pressure increase rate

Answer 19

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

Question 20

What does the maxwell boltzmann distribution curve look like when we increase concentration

Answer 20

• shape of the curve does not change ( peak is at same energy )
  so EMP and mean energy do not change
• The curves will be higher
• area under the curves will be greater because there are more particles

Question 21

how do catalysts increase the rate

Answer 21

catalysts provide an alternative route or mechanism with a lower activation energy .
If activation energy is lower , more particles will have energy higher than the activation energy
- higher frequency of successful collisions

Question 22

how does the maxwell boltzmann distribution curve change when a catalyst is involved

Answer 22

activation energy shifts to the left

Question 23

how can rate be measured in experiments

Answer 23

• how long it takes for precipitate to form
• amount of mass lost
• volume of gas produced

Question 24

what is the experiment of how long it takes for a precipitate to form

Answer 24

• place a cross on paper and time how long it takes for the cross to disappear
• problem = this is difficult to know when exactly the cross disappears
• try to use the same observer to reduce errors

Question 25

what is the experiment for the amount of mass lost

Answer 25

• for reactions that produce a gas
  place reaction in balance and measure the mass loss as gas is lost
• fairly accurate method however use a fume cupboard if gas is harmful or toxic

Question 26

what is the volume of gas experiment

Answer 26

another way of measuring the rate of a gas is produced
- measure the amount of gas louder using a gas syringe
- measure this over a specified time