3.2 Controlling the Rate

Question 1

What happens if reaction rate is not controlled in industrial processes?

Answer 1

• if the rate is too low then the process will not be economically viable
• if the rate is too high then there will be a risk of explosion

Question 2

What is relative reaction rate?

Answer 2

the rate of reaction at any one particular point in time.

Question 3

Use collision theory to explain the effects of concentration on reaction rate

Answer 3

• as the concentration of a reactant increases the reactant particles are pushed closer together
• increasing the rate of collisions
• there will be more successful collisions
• increasing the reaction rate

Question 4

Use collision theory to explain the effects of pressure on reaction rate

Answer 4

• as the pressure of a reaction mixture increases, the reactant particles are pushed closer together
• increasing the rate of collisions
• giving rise to more successful collisions
• resulting in the reaction rate increasing

Question 5

use collision theory to explain the effects of surface area on reaction rate

Answer 5

• as the surface of a reactant increases (particle size decreases)
• the area of contact between the reactants increases
• increasing the rate of collisions between reactant particles
• more successful collisions
• reaction rate will increase

Question 6

Use collision theory to explain the effects of temperature on reaction rate

Answer 6

• higher temperatures particles will have more kinetic energy
• therefore will collide with greater force
• more particles will have the required activation energy
• more successful collisions
• greater rate of reaction.

Question 7

What is temperature?

Answer 7

the average kinetic energy of the particles in a substance

Question 8

Use collision theory to explain the effects of collision geometry on reaction rate

Answer 8

-particles must collide with the correct collision geometry for a successful collision to occur (so the activated complex can be formed)

Question 9

What is enthalpy change?

Answer 9

the energy difference between the products and the reactants

Question 10

What is the enthalpy change for an exothermic reaction?

Answer 10

negative

Question 11

What is the enthalpy change for an endothermic reaction?

Answer 11

positive

Question 12

What is the activation energy for a reaction?

Answer 12

the minimum kinetic energy required by colliding particles to form an activated complex

Question 13

What is the activated complex?

Answer 13

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

Question 14

What does a catalyst do in a chemical reaction?

Answer 14

provides an alternate reaction pathway with a lower activation energy

Question 15

What can a potential energy diagram be used for?

Answer 15

-to show the effect of a catalyst on activation energy

Question 16

What can energy distribution diagrams be used for?

Answer 16

to explain the effect of changing temperature on the kinetic energy of particles and reaction rate

Question 17

Explain the effect of temperature in terms of a change in the number of particles with energy greater than the activation energy

Answer 17

• as the temperature increases the reactant particles have a larger kinetic energy
• therefore more particles have the required activation energy
• increasing the rate of reaction

Question 18

Explain the effect of adding a catalyst in terms of change in the number of particles with energy greater than the activation energy

Answer 18

• addition of a catalyst lowers the activation energy
• more particles have sufficient energy to react
• increasing the rate of reaction