Kinetics Flashcards
What is the kinetics script
A greater number of successful collisions per unit time.
Successful collision are when particles collide in the correct
orientation….
…with an energy greater than the activation energy
What does the total area under the curve represent?
The total number of molecules
This must remain constant unless you add particles.
How does temp increase the rate of reaction
Particles have more kinetic energy
So are moving faster
So a greater number of successful collisions per unit time.
Successful collusion are when particles collide in the correct
orientation….
…with an energy greater than the activation energy
How does concentration affect the rate of reaction.
More particles
In the same unit volume
Particles are closer together
So a greater number of successful collisions per unit time.
Successful collusion are when particles collide in the correct
orientation….
…with an energy greater than the activation energy
What can pressure ONLY affect
Gases
How does pressure affect the rate of reaction
Same number of particles in a smaller volume
Particles are therefore closer together
So a greater number of successful collisions per unit time.
Successful collusion are when particles collide in the correct
orientation….
…with an energy greater than the activation energy
What state of matter does surface area only affect
Solid
How does increasing surface area affect the rate of reaction
More particles are exposed and available t react.
So a greater number of successful collisions per unit time.
Successful collusion are when particles collide in the correct
orientation….
…with an energy greater than the activation energy
Explain the difference between a hetro and homogeneous catalyst
Heterogeneous: different physical state to the reactants.
Homogenous: has the same physical state as the reactants.
Explain how hetrogeneous catalyst works
Adsorption: weak bonds form between the reactants and the catalyst (this weakens the covalent bonds between molecule making it easier to break).
Reaction takes place.
Desorption: product molecules released from the surface.
EG the harbour process
Why is using a catalyst beneficial (from a business view)
Using less energy so (overhead) costs drop.
And we can use the catalyst again
What does a catalyst do
Lowers the activation energy by providing an alternate reaction pathway without being used up.
So a greater number of successful collisions per unit time.
Successful collusion are when particles collide in the correct
orientation….
…with an energy greater than the activation energy
How does a homogeneous catalyst work
Then catalyst reacts with a reactant to form an intermediate and then the catalyst is reformed again.
Producing an intermediate gives a smaller activation energy overall. (Two humps on a enthalpy graph)
Eg (happens in esters)
Where is the most probable energy on the Maxwell-Boltzmann distribution curve
Where the peak is
Where does the graph start
At the origin as NO particle has zero energy.
When we add a catalyst what happens to the M-B distribution curve
He curve doesn’t change but the activation energy line shifts to the LEFT.
Explain using M-B distribution curve why rate of reaction increases when we use a catalyst
A greater PROPORTION of particles are colliding with an energy greater than the activation energy.
What does LOWERING the temp do the M-B distribution curve
The graph will have a HIGHER hump and to the LEFT.
Activation energy stays the same (just the line is lower as less proportion particles reacting with energy greater than Ea) the most probable energy shifts to the left.
Area stays the same
What does increasing the temp do to the graph
Hump would be lower and shift to the right.
Activation line doesn’t change BUT there is a greater proportion particles colliding with energy greater than the activation energy (most probable energy shifts to the RIGHT)
Does pressure affect the shape of the M-B curve
NO it doesn’t change the energy of the particles.
What is the ONLY thing that will change the SHAPE of the M-B curve
Temp
And the number of molecules is proportion to its size.
Is the mean energy of molecules greater than the most probable energy of the molecules
Yes as mean energy lies slightly to the right of the most probable energy.
What does a Maxwell boltzmann curve show
distribution curves show how available energy is distributed among molecules in a gaseous system.
What is the activation energy
The minimum amount of energy colliding particles must have in order to react together.
In order to figure out distributions what did Maxwell and Boltzmann have to do .
Had to model gases as ideal gases, assuming gases are tiny spheres that bump into each other with elastic collisions.
What happens to the M-B curve if the concentration doubles
The area under the curve also doubles
As they are proportional
BUT the average energy of the molecules DOESN’T CHANGE
For Ea : As a proportion of the total molecules present, the number of molecules with the activation energy is the same (when we increase conc).
Explain what happens to the hump of the distribution curve when we increase the temp and why it happens
Increasing temp hump is lower and shifts to the right . This is because more particles gain higher kinetic energy, leading to a broader distribution and a higher proportion of particles having energy greater than the activation energy.
How do we calculate the rate of reaction
Amount of reactant used or product formed / time
What is meant by rate of reaction
The change in the amount of a reactant or product ( conc or mass) over time .(g s-1or cm3 s-1)
What’s are the different ways to measure the rate of reaction
1) timing how long it takes for precipitate to form (subjective not accurate) use sodium thioslufate and HCl
2)measuring a change in mass
3)measuring volume of gas produced (inverted cylinder or syringe)
4) we can also measure the pH change (using a pH meter)
5) colour change (colorimetry
How do we calculate the gradient
Change Y / change X
Outline a method to show that a catalyst is not used up in a reaction .
1) filter the solid (catalyst) after the reaction
2)rinse and dry the solid (catalyst )
3)reweigh the solid (to prove it has no been used up)
4) use the catalyst again, if same results it functions as a catalyst.
In the disappearing cross experiment why does the student record times to the nearest second not 0.01second
Because it is subjective judging when the cross actually disappears.
