Topic 9 - Kinetics I

Question 1

What are the two definitions of rate of reaction?

Answer 1

• How quickly the reactants are used up/ how quickly the products are formed
• The change of concentration of a reactant/product per unit time

Question 2

What are the units for rate of a reaction?

Answer 2

moldm^-3s^-1

Question 3

What type of graph can you plot to find the rate of reaction?

Answer 3

A concentration-time graph

Question 4

What are the 5 factors that affect the rate of reaction?

Answer 4

• Temperature
• Surface Area of reactant
• Concentration
• Catalyst
• Pressure

Question 5

What are the three assumptions of collision theory?

Answer 5

• The particles have to collide
• Particles must have at least the activation energy
• Particles must collide in the correct orientation

Question 6

What are the 2 different ways that changes in rate of reaction due to changing conditions can be explained?

Answer 6

• Simple collision theory
• Boltzmann distribution curve

Question 7

How would you explain the change in rate using simple collision theory when the concentration of a reactant is changed?

Answer 7

• More particles in a given volume
• More frequent collisions
• Higher rate of reaction

Question 8

How would you explain the change in rate using simple collision theory when the surface area of a reactant is changed?

Answer 8

• Particles have more kinetic energy
• Therefore, particles move faster so collide more frequently AND more particles have an energy that is greater than the activation energy of the reaction
• A greater proportion of collision are successful
• Higher rate of reaction

Question 9

How would you explain the change in rate using simple collision theory when the temperature is changed?

Answer 9

• More available particles to collide with
• Increased frequency of collisions
• Higher rate of reaction

Question 10

What does the area under the line of a Boltzmann Distribution curve show us?

Answer 10

The total number of particles

Question 11

How would you explain the change in rate using Boltmann’s distribution when the temperature is changed?

Answer 11

• The curve is shifted to the right with the peak lower but the bottom of the curve plateauing higher -> the area under the graph remains constant
• Larger area under the graph that is to the right of the activation energy line
• An increase kinetic energy of the particles
• Area under the curve above the activation energy is larger at higher temperatures so a greater proportion of particles have E >= Ea
• Increased proportion of successful collisions
• Particles are also moving faster so there si an increased frequency of collisions

Question 12

How would you explain the change in rate using Boltmann’s distribution when a catalyst is added?

Answer 12

• Catalyst provides an alternate pathway with a lower activation energy for a reaction to proceed via
• Increased area to the right of the activation energy line meaning that a greater proportion of particles have the required activation energy
• Increased proportion of successful collisions

Question 13

How do you find the rate of reaction at different points on a concentration - time graph?

Answer 13

Take the gradient at that point

Question 14

What are the two types of catalyst?

Answer 14

Heterogenous and Homogenous

Question 15

What is the definition of a heterogenous catalyst?

Answer 15

The reactants and catalyst are in a different physical state

Question 16

What is the definition of a homogenous catalyst?

Answer 16

The reactants and catalyst are in the same physical state

Question 17

Describe how heterogenous catalysts work?

Answer 17

• The reactant molecule approaches the catalyst and is adsorped onto its active site
• The bonds are weakened allowing rearrangement of atoms to occur
• The products are released from the surface - desorped

Question 18

What is the heterogenous catalyst used in the Haber process?

Answer 18

Iron

Question 19

What is the heterogenous catalyst used in the contact process?

Answer 19

V2O5

Question 20

What is the heterogenous catalyst used in Hydrogenation?

Answer 20

Nickel

Question 21

In what way do catalysts benefit the environment?

Answer 21

• Lower temperatures can be used for reactions
• Less energy is required therefore, less GHG’s produced

Question 22

In what away are catalyst economically beneficial?

Answer 22

• Allows lower temperatures to be used
• Less money spent on heating
• The catalyst can be reused therefore, you don’t have to keep repurchasing it