Controlling the Rate

Question 1

What will happen if the rate is too low?

Answer 1

The process will not be economically viable

Question 2

What will happen is the rate is too high?

Answer 2

The process might not be safe - there is a risk of explosion

Question 3

What are the 3 things that need to happen for a chemical reaction to occur?

Answer 3

1. The reacting particles must collide
2. Collisions must have sufficient energy
3. The reacting particles must have the correct orientation or collision geometry

Question 4

What is activation energy?

Answer 4

The minimum kinetic energy required for a chemical reaction to occur

Question 5

How is an activated complex formed?

Answer 5

When reactant particles collide with the required activation energy

Question 6

What is an activated complex?

Answer 6

A high energy, unstable intermediate

Question 7

How does particle size affect the rate of reaction?

Answer 7

Decreasing the particle size will increase the rate of reaction because the surface area of reactant molecules would increase

An increase in surface area means there is more area for collisions to occur, therefore there is a greater chance of successful collisions occurring.

The smaller the particle size, the faster the reaction

Question 8

How does concentration affect the rate of reaction?

Answer 8

The higher the concentration of reactants, the faster the reaction.

This is because a highly concentrated reaction will have more reacting particles, meaning there are more particles which can potentially collide with each other.

Therefore, there is a greater chance of successful collisions, and so the higher the concentration the faster the reaction.

Question 9

What is enthalpy?

Answer 9

The heat energy stored in a substance

Question 10

What is enthalpy change?

Answer 10

The difference between the enthalpy of products and reactants, it is measured in kJmol^-1

Question 11

How is enthalpy change measured?

Answer 11

△H = H products - H reactants

Question 12

What will the △H of an endothermic reaction always be?

Answer 12

Positive - the energy of the products is more than the energy of reactants

Question 13

What will the △H of an exothermic reaction always be?

Answer 13

Negative - the energy of the products is less than the energy of the reactants

Question 14

What does a catalyst do?

Answer 14

Provides an alternative pathway for the reaction with a lower activation energy, speeding up the reaction

Question 15

What effect does a catalyst have on the enthalpy change?

Answer 15

It has no effect

Question 16

What is the relative rate formula?

Answer 16

reaction rate = 1/t

(units are in s^-1)

Question 17

How do you work out the time from the relative rate formula?

Answer 17

Time = 1/reaction rate

Question 18

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

Answer 18

Increasing the pressure increases the rate because the particles have less space to move so there is a greater chance for collisions to occur.

Question 19

What is temperature a measure of?

Answer 19

The average kinetic energy of all particles

Question 20

What effect does increasing temperature have on the rate of reaction?

Answer 20

Increasing the temperature increases the rete because as we increase the temp, we increase the energy the particles have which cause the collision which occur to have the energy required to react.

(more particles will have energy equal to or greater than the activation energy)

Question 21

How does increasing temperature look on a potential energy diagram?

Answer 21

If we increase the temperature, the graph moves to the right and gets lower