Kinetics 1

Question 1

Collision theory

Answer 1

For 2 reactant particles to react:
Particles must collide at the right orientation
Collisions must have sufficient energy ‘Ea’

Question 2

Activation energy

Answer 2

For a reaction to start an energy threshold needs to be met

Question 3

Energy profile diagram

Answer 3

A diagram which shows the enthalpy over progress of reaction
As well as an arrow representing the activation energy

Question 4

Bonds broken over an energy profile diagram

Answer 4

Bonds begin to stretch as energy increases
At the top (at activation energy) the bonds are broken because they overcame energy barrier to react

Question 5

What is the rate of reaction

Answer 5

The rate at which reactants are converted to products
Or products are formed from reactants

Question 6

What can rate of reaction be measured by?

Answer 6

The rate at which reactants are used up
The rate at which products are formed from

Question 7

How to calculate rate of reaction?

Answer 7

Change in concentration of product formed/reactant used up
——————————————
Change in time

Question 8

Unit of rate of reaction

Answer 8

g s⁻¹
mol s⁻¹

Question 9

Factors affecting the rate?

Answer 9

Temperature
Surface area
Catalysts
Concentration of reactants
Pressure of gas reactants

Question 10

A maxwell-Boltzmann distribution

Answer 10

Plotting a graph to show the distribution of energy across the number of particles involved in a reaction

Question 11

What does a Maxwell-Boltzmann distribution look like?

Answer 11

Number of molecules = y axis
Ek of molecules = x axis
Distorted bell curve shifted to the left which starts at 0 but never reaches 0 on other end
Eaon the right end

Question 12

Why do Maxwell-Boltzmann distributions always start at 0,0?

Answer 12

Because no particles will have 0 energy, so shows absence of particles

Question 13

Where on a Maxwell-Boltzmann graph show the number of particles which react?

Answer 13

The area under the bit of the graph passing the activation energy showing they have collided with successful energy (over the Ea)

Question 14

Does the Maxwell-Boltzmann graph ever hit 0 on the other side?

Answer 14

No, only runs parallel to x axis because all particles must have some level of energy

Question 15

What does the area under a Maxwell-Boltzmann graph show?

Answer 15

The total number of particles

Question 16

How does increasing concentration affect rate of reaction?

Answer 16

More particles are in a given volume thus are more are able to react
So more collisions occur
So more successful collisions which overcome Ea occur
=increases rate of reaction

Question 17

How can we measure the affect of surface area on rate of reaction?

Answer 17

Using marble chips of different sizes by measuring volume of CO2 gas collected when reacted with HCl

Question 18

Effect of concentration on maxwell-Boltzmann distribution?

Answer 18

Increases along the y axis but no move in the curve along x axis
Because there is a higher number of particles in a given volume thus more particles collide with sufficient energy

Question 19

How does increasing temperature affect the rate of reaction?

Answer 19

Particles have more kinetic energy so collide more
Therefore greater proportion of molecules collide with sufficient energy to surpass Ea

Question 20

Effect of temperature on a maxwell-Boltzmann distribution?

Answer 20

Graph is moved to the right showing that higher number of particles have more energy and also more particles surpass Ea
But because there is still same no. Of particles, the area must be the same so offset this by the peak being lower at higher temps

Question 21

What is the effect of pressure on rate of reaction?

Answer 21

There are more gaseous molecules per unit volume by increasing pressure
So this increases frequency of collisions between reactant molecules
Thus more collisions overcome the activation energy and can react

Question 22

Effect of pressure on maxwell-Boltzmann distribution