Controlling the Rate

Question 1

Explain why reaction rates must be controlled in industrial processes.

Answer 1

• If reaction rates are too low, the process will be not economical.
• If reaction rates are too high, there will be a risk of explosion.

Question 2

How do you calculate the rate of reaction?

Answer 2

• Rate = 1/t
• Rate = Δ quantity/Δ time

Question 3

How does concentration affect the rate of reaction?

Answer 3

Increased concentration leads to more particles in the reaction, resulting in higher chance of collisions.

Question 4

How does particle size affect the rate of reaction?

Answer 4

decreasing the particle size allows more space for collisions due to increase in surface area.

Question 5

How does temperature affect the rate of reaction?

Answer 5

• the particles have more kinetic energy so move faster, making collisions more likely.
• more of them will reach the activation energy.

Question 6

How does pressure affect the rate of reaction?

Answer 6

if pressure is increased (for gaseous reactants) there are more reactant particles for a given volume so there will be more collisions.

Question 7

How does geometry affect the rate of reaction?

Answer 7

particles must collide with the correct geometry for the reaction to be successful.

Question 8

What is enthalpy change?

Answer 8

enthalpy change is the difference in energy between the products and reactants.

Question 9

Describe an exothermic reaction and it’s enthalpy

Answer 9

energy of the product is less than the energy of reactants (energy given out to surroundings) giving a -ve enthalpy.

Question 10

Describe an endothermic reaction and it’s enthalpy

Answer 10

energy of products is more than the energy of reactants (energy taken from surroundings), giving a +ve enthalpy.

Question 11

What is activation energy?

Answer 11

• Activation energy (Ea) is the minimum energy required by the particles to form an activated complex.
• If colliding particles don’t have the activation energy, the collision will not take place.
• On a potential energy diagram, the Ea is the difference between the highest energy and the energy of reactants.

Question 12

What is the activated complex?

Answer 12

the unstable arrangement of atoms formed at the top of the potential energy barrier.

Question 13

How do catalysts affect activation energy?

Answer 13

• Catalysts provide an alternative pathway for reactants.
• The alternative pathway will have a lower activation energy.