Kinetics I

Question 1

Describe the effect of changing concentration on Rate of Reaction

Answer 1

Particles can only react when they collide.
Changing concentration varies number of particles in each cm3
This changes the frequency of collisions and therefore the rate of reaction

Question 2

Describe the effect of changing pressure on Rate of Reaction

Answer 2

Only affects Gases
Increasing the pressure of a gas is exactly the same as increasing its concentration. If you have a given mass of gas, the way you increase its pressure is to squeeze it into a smaller volume. If you have the same mass in a smaller volume, then its concentration is higher.

Question 3

Describe the effect of changing temperature on Rate of Reaction

Answer 3

Particles can only react when they collide.
If you heat a substance, the particles move faster and so collide more frequently.
That will speed up the rate of reaction.

Question 4

Describe the effect of changing surface area on Rate of Reaction

Answer 4

Collisions at the surface are more probable. More collisions between reactant molecules per unit time

Question 5

Describe, ‘Activation Energy’

Answer 5

Reactions only take place when collisions take place with sufficient energy

Question 6

In terms of the Maxwell-Boltzmann Distribution Graph, describe the effect of increasing temperature

Answer 6

Modal Energy(top of the peak) shifts to the right
Height is shorter than original curve
Results in greater proportion of particles with energy greater than activation energy(area is bigger)
Therefore the reaction will be quicker

Question 7

Describe the use of a solid (heterogeneous) catalyst

Answer 7

eg. Alkene + H2 gas with a nickel catalysts
1. Adsorption of the reactants to the surface of the catalyst
2. Bonds within the reactants are weakened, less energy required to break them. Active Sites on the catalyst bind reactants, greater chance of collision.(traps them on the catalyst)
3. Desorption of products

Question 8

What are the economic benefits of using a catalyst

Answer 8

Less energy is needed due to a lower activation energy
Cheaper due less less money spent on energy

Question 9

In terms of the Maxwell-Boltzmann Distribution Graph, describe the effect of decreasing temperature

Answer 9

Modal Energy(top of the peak) shifts to the left
Height is taller
Results in a smaller proportion of particles(area) with energy greater than activation energy
Therefore the reaction will be slower

Question 10

Describe how a catalyst works

Answer 10

A chemical that speeds up rates of reaction without being used up.
Provides an alternate pathway with lower activation energy.

Question 11

In terms of the Maxwell-Boltzmann Distribution Graph, describe the effect of adding a catalyst

Answer 11

Lowers activation energy line
Greater proportion of particles(area) are greater than the activation energy
Therefore the reaction will be quicker