A-LEVEL Chemistry: 3.1.5: Kinetics (ChemRevise)

Question 1

What is the ‘Collision Theory’?

Answer 1

The Collision Theory is that Reactions Can Only Occur when Collisions Take Place Between Particles with Sufficient Energy (Activation Energy).

Question 2

What is ‘Activation Energy (Ea)’?

Answer 2

The Activation Energy (Ea) is the Minimum Energy which Particles Need to Collide & Start a Reaction.

Question 3

What is the ‘Maxwell-Boltzmann Distribution’?

Answer 3

The Maxwell-Boltzmann Distribution Shows the Spread of Energies that Molecules of a Gas or Liquid have at a Particular Temperature.

Question 4

Explain the ‘Maxwell-Boltzmann Distribution Curve’:

Answer 4

Study this part on the chem revise page:
https://chemrevise.org/wp-content/uploads/2023/02/1.5-revision-guide-reaction-kinetics-aqa.pdf

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Question 5

In the ‘Maxwell-Boltzmann Distribution Curve’, why do a few Particles have Low Energies?

Answer 5

Because Some Collisions Cause Some Particles to Slow Down.

Question 6

In the ‘Maxwell-Boltzmann Distribution Curve’, what is ‘Emp’?

Answer 6

The Most Probable Energy of Particles (not the Same as Mean Energy).

Question 7

What does the Area Under the Graph Represent in the ‘Maxwell-Boltzmann Distribution Curve’?

Answer 7

The Total Number of Particles Present.

Question 8

In the ‘Maxwell-Boltzmann Distribution Curve’, Only a Few Particles have Energy Greater than…

Answer 8

the Activation Energy.

Question 9

In the ‘Maxwell-Boltzmann Distribution Curve’, why should the Energy Distribution Never Meet the x-axis?

Answer 9

Because there is no Maximum Energy for Molecules.

Question 10

In the ‘Maxwell-Boltzmann Distribution Curve’, the Mean Energy of the Particles is Not at the…

Answer 10

Peak of the Curve.

Question 11

In the ‘Maxwell-Boltzmann Distribution Curve’, the Energy Distribution Must go Through the ___. Why is this?

Answer 11

Origin.
Because there are No Molecules with No Energy (Origin = 0,0).

Question 12

How Can a Reaction go to Completion if Few Particles have Energy Greater than Ea (Activation Energy)?

Answer 12

Because Particles Can Gain Energy Through Collisions with Other Particles.

Question 13

In the ‘Maxwell-Boltzmann Distribution Curve’, as the Temperature Increases, …

Answer 13

The Distribution Shifts Towards having More Molecules with Higher Energies.

Question 14

In the ‘Maxwell-Boltzmann Distribution Curve’, what happens at Higher Temperatures?

Answer 14

At Higher Temperatures, both the Emp & the Mean Energy Shift to Higher Energy Values, Although the Number of Molecules with those Energies Decrease.

Question 15

In the ‘Maxwell-Boltzmann Distribution Curve’, the Total Area Under the Graph should… Why is this?

Answer 15

Remain Constant.
Because the Total Number of Particles is Constant.

Question 16

In the ‘Maxwell-Boltzmann Distribution Curve’, at Higher Temperatures, the Molecules have a ___ Range of ___ than at ___ ___.

Answer 16

Wider, Energies, Lower Temperatures.

Question 17

What is the ‘Rate of Reaction’?

Answer 17

The Rate of Reaction is the Change in Concentration of a Substance in Unit Time.
(Usual Unit is moldm^-3s^-1)

Question 18

When a Graph of Concentration of Reactant vs Time is Plotted, what does the Gradient of the Curve Represent?

Answer 18

The Rate of Reaction.

Question 19

What is the ‘Initial Rate’?

Answer 19

The Initial Rate of a Reaction is the Rate at the Start of the Reaction, when it is Fastest.

Question 20

What Graphs Can be Used to Calculate the Rate of a Reaction? How?

Answer 20

Graphs of Concentration of Reactants or Products / Time.
By Drawing a Tangent to the Curve (at Different Times), & Calculating the Gradient of the Tangent.

Question 21

In the Experiment Between Sodium Thiosulfate & Hydrochloric Acid, we Usually Measure the Rate of Reaction as…
Why Can we use this?

Answer 21

1/Time.
Because we Can Assume that the Amount of Sulphur Produced is Fixed & Constant.

Question 22

Explain what happens in Reactions where the Particles are in Higher Concentrations/Higher Pressures?

Answer 22

There are More Particles Per Unit Volume, & so the Particles Collide with a Greater Frequency, & there Will be a Higher Frequency of Effective Collisions.

Question 23

If a RoR Question Mentions a Doubling of Concentration/Rate, then make sure you…

Answer 23

Mention Double the Number of Particles Per Unit Volume, & Double the Frequency of Effective Collisions.

Question 24

In a Reaction, if the Concentration of Particles Increases, what happens to the Shape of the ‘Maxwell-Boltzmann Distribution Curve’? (3)

Answer 24

-The Shape of the Energy Distribution Curves Do Not Change.

-The Curves Will be Higher Up.

-The Area Under the Curves Will Increase, because there are More Particles.

Question 25

Different Volumes of the Same Initial Concentrations Will Have… (2)

Answer 25

-The Same Initial Rate of Reaction (if other Conditions are the Same).

-But they Will End at Different Amounts.

Question 26

The Higher the Concentration/Temperature/Surface Area, the ___ the Rate of Reaction, & the ___ the Gradient.

Answer 26

Faster, Steeper.

Question 27

The Higher the Concentration of Particles, the ___ the Rate of Reaction, & the ___ the Gradient.

Answer 27

Faster, Steeper.

Question 28

The Higher the Temperature, the ___ the Rate of Reaction, & the ___ the Gradient.

Answer 28

Faster, Steeper.

Question 29

The Greater the Surface Area Available, the ___ the Rate of Reaction, & the ___ the Gradient.

Answer 29

Faster, Steeper.

Question 30

Explain the Effect of ‘Increasing the Temperature’ on the Rate of Reaction: (3)

Answer 30

-At Higher Temperatures, the Energy of the Particles Increases.

-The Particles Collide More Frequently, with Higher Energies, Greater than the Activation Energy.

-More Successful High-Energy Collisions Result in an Increased Rate of Reaction.

Question 31

As the Temperature Increases, what does the Maxwell-Boltzmann Distribution Graph Show? (2)

Answer 31

-A Significantly Larger Number of Particles have Energy Greater than the Activation Energy.

-The Frequency of Successful Collisions Increases.

Question 32

Explain the Effect of ‘Increasing Surface Area’ on the Rate of Reaction:

Answer 32

Increasing Surface Area Will Cause Successful Collisions to Occur More Frequently Between the Reactant Particles, & this Increases the Rate of Reaction.

Question 33

What do ‘Catalysts’ do?

Answer 33

Catalysts Increase the Rate of Reaction Without getting Used Up.

Question 34

How do ‘Catalysts’ Work?

Answer 34

Catalysts Increase the Rate of Reaction Without getting Used Up.

They do this by Providing an Alternative Reaction Pathway, with Lower Activation Energy.

Question 35

Catalysts Increase the Rate of Reaction Without getting Used Up. How do they do this?

Answer 35

They do this by Providing an Alternative Reaction Pathway, with Lower Activation Energy.

Question 36

If the Activation Energy of a Reaction is Lower, ___ Particles Will have ___. What does this Mean?

Answer 36

More, Energy.
This Means that there Will be a Higher Frequency of Effective Collisions. The Rate of Reaction Will be Faster.

Question 37

With a Lower Activation Energy, ___ Particles have…
Hence, the Rate of Reaction…

Answer 37

More.
Energy Greater than the Activation Energy.
Increases.