Kinetics

What is rate of reaction?

How fast reactants are changed into products

What is collision theory and what does it depend on?

Collision theory states that the rate of reaction depends on:

1. How often reacting particles collide with each other - the more collisions the faster the rate

2. The energy transferred during a collision. Particles have to collide with enough energy for a collision to be successful

What is activation energy?

The minimum amount of kinetic energy needed for particles to react

What factors affect rate of reaction?

1. Temperature

2. Catalysts

3. Concentration

4. Surface area

5. Pressure of gas

How does increasing the temperature affect the rate of reaction?

Increased energy and frequency of collisions

How does adding catalysts affect the rate of reaction?

It lowers the activation energy

How does increasing the concentration, surface area and pressure affect the rate of reaction?

They increase the frequency of collisions

How do you work out the rate of reaction?

Change in concentration of product/reactant

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time

What’s happening at points A,B,C,D,E and F?

• A = The curves starts at (0,0) as no particles have 0ke

• B = A few molecules are moving slowly

• C = The peak of the curve represents the most likely energy of any single molecule

• D = The mean energy of all molecules is a bit right of the peak

• E = most move at moderate speed

• F = These are the only ones that can react?

What does the area under the graph represent?

The area is equal to the number of molecules present

How does temperature affect the distribution?

• They only cross once

• Peak shifts to the right

• Most particles under the activation energy

Height lowers as areas must be equal.

A small change in temperature would lead to more frequent collisions

How does concentration affect the distribution?

Shifts it upwards

What factor does not affect the distribution?

Gas pressure

What is a catalyst?

Increases the rate of reaction by providing an alternative pathway with a lower activation rate

• They partake in chemical reactions but are put together again at the end of it

How do catalysts affect the Maxwell-Boltzmann distribution?

The molecules still have the same amount of energy so the distribution does not change

What is a homogeneous catalyst?

In the same phase as the reactants

What is a heterogeneous catalyst?

In different phase as the reactants

What is adsorption?

Molecules or ions gather on the surface

How do catalysts work?

1. Reactants are adsorbed onto the surface

2. Bonds are weakened and broken

3. New bonds are formed

4. Desorption (products diffuse away)

What are often used as catalysts?

Transition metals are often used and layed thinly over a ceramic honeycomb

What are the environmental and economic impacts of using a catalyst?

• They save money in industrial processes

• The reactions can occur at lower temperatures so less fuel is needed hence fewer emissions from fuels

• By providing a alternative pathway this gives them a higher atom economy: so less raw materials will be needed and less waste products