Rates of reaction collision theory

Question 1

Define rate of reaction

Answer 1

The rate of reaction is the change in concentration of a reactant or a product in a given time.

Question 2

What is the equation for rate of reaction?

Answer 2

rate= change in concetration/time

units: mol dm^-3s^-1

Question 3

Explain how the rate of reaction changes with the concetration of the reactants.

Answer 3

1) At the start of a reaction, each reaction has its greatest concentration- the rate of reaction is at its fastest.
2) As the reaction proceeds the concentrations of the reactants decrease- the rate of reaction slows down
3) When one of the reactants has been used up the rate becomes zero.

Question 4

Name the several factors that can alter the rate of chemical reaction.

Answer 4

• Temperature
• Pressure, when the reactants are gases
• Concentration
• Surface area
• Adding a catalyst

Question 5

Explain the certain conditions that are required for a reaction to take place.

Answer 5

• The molecules must have sufficient energy to overcome the activation energy.
• The molecules most collide in the correct orientation.

For example: In a reaction: A + BC —-> AB + C

A must collide into the B side of the molecule for the reaction to take place. If A collides into C nothing happens.

Question 6

Explain why if the concentrations of the reactants are increased, the rate of reaction also increases.

Answer 6

• Increased concentrations give more molecules in the same volume.
• The molecules will be closer together and there is a greater change of the molecules colliding.
• Collisions will be more frequent- more collisions will occur in a certain length of time.

So, for a particular length of time more collisions will take place and there will be more collisions with energy greater than the activation energy.There will be more frequent collisions and the rate of reaction will increase.

Question 7

Explain the effect of pressure on reaction rate.

Answer 7

When the pressure of gas is increased, the molecules are pushed closer together.

• The same number of molecules occupy a smaller volume.
• For a gaseous reaction, increasing the pressure is the same as increasing the concetration.

So, for a particular length of time more collisions will take place and there will be more collisions with energy greater than the activation energy.There will be more frequent collisions and the rate of reaction will increase.