A-LEVEL Chemistry: 3.1.5: Kinetics (ChemRevise) Flashcards
What is the ‘Collision Theory’?
The Collision Theory is that Reactions Can Only Occur when Collisions Take Place Between Particles with Sufficient Energy (Activation Energy).
What is ‘Activation Energy (Ea)’?
The Activation Energy (Ea) is the Minimum Energy which Particles Need to Collide & Start a Reaction.
What is the ‘Maxwell-Boltzmann Distribution’?
The Maxwell-Boltzmann Distribution Shows the Spread of Energies that Molecules of a Gas or Liquid have at a Particular Temperature.
Explain the ‘Maxwell-Boltzmann Distribution Curve’:
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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In the ‘Maxwell-Boltzmann Distribution Curve’, why do a few Particles have Low Energies?
Because Some Collisions Cause Some Particles to Slow Down.
In the ‘Maxwell-Boltzmann Distribution Curve’, what is ‘Emp’?
The Most Probable Energy of Particles (not the Same as Mean Energy).
What does the Area Under the Graph Represent in the ‘Maxwell-Boltzmann Distribution Curve’?
The Total Number of Particles Present.
In the ‘Maxwell-Boltzmann Distribution Curve’, Only a Few Particles have Energy Greater than…
the Activation Energy.
In the ‘Maxwell-Boltzmann Distribution Curve’, why should the Energy Distribution Never Meet the x-axis?
Because there is no Maximum Energy for Molecules.
In the ‘Maxwell-Boltzmann Distribution Curve’, the Mean Energy of the Particles is Not at the…
Peak of the Curve.
In the ‘Maxwell-Boltzmann Distribution Curve’, the Energy Distribution Must go Through the ___. Why is this?
Origin.
Because there are No Molecules with No Energy (Origin = 0,0).
How Can a Reaction go to Completion if Few Particles have Energy Greater than Ea (Activation Energy)?
Because Particles Can Gain Energy Through Collisions with Other Particles.
In the ‘Maxwell-Boltzmann Distribution Curve’, as the Temperature Increases, …
The Distribution Shifts Towards having More Molecules with Higher Energies.
In the ‘Maxwell-Boltzmann Distribution Curve’, what happens at Higher Temperatures?
At Higher Temperatures, both the Emp & the Mean Energy Shift to Higher Energy Values, Although the Number of Molecules with those Energies Decrease.
In the ‘Maxwell-Boltzmann Distribution Curve’, the Total Area Under the Graph should… Why is this?
Remain Constant.
Because the Total Number of Particles is Constant.
In the ‘Maxwell-Boltzmann Distribution Curve’, at Higher Temperatures, the Molecules have a ___ Range of ___ than at ___ ___.
Wider, Energies, Lower Temperatures.
What is the ‘Rate of Reaction’?
The Rate of Reaction is the Change in Concentration of a Substance in Unit Time.
(Usual Unit is moldm^-3s^-1)
When a Graph of Concentration of Reactant vs Time is Plotted, what does the Gradient of the Curve Represent?
The Rate of Reaction.
What is the ‘Initial Rate’?
The Initial Rate of a Reaction is the Rate at the Start of the Reaction, when it is Fastest.
What Graphs Can be Used to Calculate the Rate of a Reaction? How?
Graphs of Concentration of Reactants or Products / Time.
By Drawing a Tangent to the Curve (at Different Times), & Calculating the Gradient of the Tangent.
In the Experiment Between Sodium Thiosulfate & Hydrochloric Acid, we Usually Measure the Rate of Reaction as…
Why Can we use this?
1/Time.
Because we Can Assume that the Amount of Sulphur Produced is Fixed & Constant.
Explain what happens in Reactions where the Particles are in Higher Concentrations/Higher Pressures?
There are More Particles Per Unit Volume, & so the Particles Collide with a Greater Frequency, & there Will be a Higher Frequency of Effective Collisions.
If a RoR Question Mentions a Doubling of Concentration/Rate, then make sure you…
Mention Double the Number of Particles Per Unit Volume, & Double the Frequency of Effective Collisions.
In a Reaction, if the Concentration of Particles Increases, what happens to the Shape of the ‘Maxwell-Boltzmann Distribution Curve’? (3)
-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.
Different Volumes of the Same Initial Concentrations Will Have… (2)
-The Same Initial Rate of Reaction (if other Conditions are the Same).
-But they Will End at Different Amounts.
The Higher the Concentration/Temperature/Surface Area, the ___ the Rate of Reaction, & the ___ the Gradient.
Faster, Steeper.
The Higher the Concentration of Particles, the ___ the Rate of Reaction, & the ___ the Gradient.
Faster, Steeper.
The Higher the Temperature, the ___ the Rate of Reaction, & the ___ the Gradient.
Faster, Steeper.
The Greater the Surface Area Available, the ___ the Rate of Reaction, & the ___ the Gradient.
Faster, Steeper.
Explain the Effect of ‘Increasing the Temperature’ on the Rate of Reaction: (3)
-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.
As the Temperature Increases, what does the Maxwell-Boltzmann Distribution Graph Show? (2)
-A Significantly Larger Number of Particles have Energy Greater than the Activation Energy.
-The Frequency of Successful Collisions Increases.
Explain the Effect of ‘Increasing Surface Area’ on the Rate of Reaction:
Increasing Surface Area Will Cause Successful Collisions to Occur More Frequently Between the Reactant Particles, & this Increases the Rate of Reaction.
What do ‘Catalysts’ do?
Catalysts Increase the Rate of Reaction Without getting Used Up.
How do ‘Catalysts’ Work?
Catalysts Increase the Rate of Reaction Without getting Used Up.
They do this by Providing an Alternative Reaction Pathway, with Lower Activation Energy.
Catalysts Increase the Rate of Reaction Without getting Used Up. How do they do this?
They do this by Providing an Alternative Reaction Pathway, with Lower Activation Energy.
If the Activation Energy of a Reaction is Lower, ___ Particles Will have ___. What does this Mean?
More, Energy.
This Means that there Will be a Higher Frequency of Effective Collisions. The Rate of Reaction Will be Faster.
With a Lower Activation Energy, ___ Particles have…
Hence, the Rate of Reaction…
More.
Energy Greater than the Activation Energy.
Increases.
Whats
-MP: The Enrgy at which therea re the most particles with tha tenrergy
-Mean Energy: Total Energy / Total Particles (will awlats be abn it to the t
