OZ 2 - Kinetics

Question 1

What is the activation enthalpy of a reaction?

Answer 1

The activation enthalpy is the minimum kinetic energy required by the molecules in a reaction for successful collisions to occur. Molecules with energies below this will not react

Question 2

What effect does increasing the pressure/concentration have on the rate of reaction?

Answer 2

Increasing the concentration/pressure increases the frequency of collisions between molecules as there are more molecules per unit volume. This increases the frequency of successful collisions and therefore the rate of reaction increases

Question 3

Why does increasing the temperature increase the rate of reaction?

Answer 3

Increasing the temperature increases the average kinetic energy of the molecules involved in the reaction, therefore a greater proportion of molecules have an energy that is greater than the activation energy, leading to more frequent successful collisions

Question 4

How does a catalyst increase the rate of reaction?

Answer 4

A catalyst provides an alternative reaction route with a lower activation energy, so that a greater proportion of molecules have kinetic energies above the activation energy

Question 5

What is a homogeneous catalyst?

Answer 5

A homogeneous catalyst is a catalyst that is the same phase as the reactants and products

Question 6

What are the initiation, propagation and termination steps for the free radical breakdown of ozone?

Answer 6

Initiation: Cl2 ==> 2Cl*
Propagation: Cl* + O3 ==> ClO* + O2
ClO* + O3 ==> 2O2 + Cl*
Termination: Cl* ==> Cl2
or 2ClO* ==> Cl2 + O2