Unit 1: Controlling the rate

Why is controlling the rate important in industrial processes

If they are too low a manufacturing process will not be economically viable

Too high and there is the risk of thermal explosion

What is activation energy?

The certain minimum kinetic energy particles must collide at to overcome the forces of repulsion between their electron clouds

What does activation energy act as

A barrier standing between the reactants and products

Finding activation energy of forward reaction

Top of graph to reactant value

Finding activation energy of reverse reaction

Activation energy of forward reaction minus enthalpy change

What does a reaction with a ‘very low barrier’ mean

It has a small activation energy and therefore the reaction will be fast and will occur spontaneously at room temperature

What does a reaction with a ‘high barrier’ mean

Extra energy must be supplied to the reactant particles to ensure that the energy of collision is greater than the activation energy

Formula for relative rate

1/time

Formula for time

1/relative rate

What does [Delta] H mean

Change in enthalpy

Why do low temperatures make colour changing reactions less reliable? And how can the issue be solved?

The colour change is too gradual (difficult to determine end point)

Start with higher temperatures

Explain how an increase in temperatrue increases the rate of reaction

Reacting particles have a greater kinetic energy meaning there is more chance of successful collisions. Therefore, increased rate of reaction.

What is pressure

A measure of how often the gas molecules collide with the walls of a container

How is pressure increased

Compressing the same number of molecules into a smaller volume

Why does a higher pressure increase rate of reaction

The higher the pressure, the more particles in a given volume, the more chance there is of successful collisions. Therefore increased rate of reaction.

Why does a higher concentration increase the rate of reaction

The higher the concentration the more particles in a given space, the more chance there is of successful collisions. Therefore increased rate.

What is enthalpy?

The energy content of a substance

Definition of enthalpy change

The net energy between, the energy required to break bonds, and the energy released when new bonds are made in a reaction.

What sign will the enthalpy change for:

an endothermic reaction

an exothermic reaction

Endothermic = positive sign

Exothermic = negative sign

How to find the enthalpy change for forwards and reverse reaction

Forwards:

Products minus reactants

Reverse:

Change sign of forwards reaction

What is activation energy

The minimum kinetic energy required by colliding molecules to form an activated complex

What is an activated complex

The unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction

State two conditions necessary for a collision to be successful (1)

Molecules must collide with energy greater than activation energy (1)

And molecules must collide with correct orientation (1)

How do catalysts speed up a reaction?

They provide an alternative reaction pathway which has a lower activation energy

Do catalysts form bonds with reacting molecules?

Yes

Do catalysts affect the enthalpy change for a reaction?

No

Will catalysed reactions have a lower potential energy on a graph or a higher potential energy?

Lower

Explain fully why increasing temperature increases the rate of a chemical reaction

Increases the number of particles with energy equal to or greater than the

activation energy (1)

Causing more successful collisions (2)