6. Chemical Kinetics

Question 1

What is rate of reaction?

Answer 1

The change in concentration of a reactant or product over time.

Question 2

What are the units of rate of reaction?

Answer 2

moldm-3s-1

Question 3

What are the assumptions of kinetic molecular theory?

Answer 3

• Particles are in constant motion.
• All collisions are elastic

Question 4

What must happen for a reaction to occur?

Answer 4

• The particles must collide with each other with sufficient energy (Ea)
• The particles must collide in the correct orientation

Question 5

What is activation energy?

Answer 5

The minimum energy needed for a reaction to occur on colliding of particles.

Question 6

What does a Maxwell-Boltzmann curve show?

Answer 6

Shows the energy distribution in a sample of molecules.

Question 7

What is the area under a Maxwell-Boltzmann curve?

Answer 7

The total number of particles.

Question 8

What factors affect the rate of reaction?

Answer 8

• Surface area
• Temperature
• Concentration
• Pressure/ volume
• Catalysts

Question 9

Why are catalysts not included in chemical equations?

Answer 9

They are not used up.

Question 10

How do catalysts work?

Answer 10

They lower the activation energy of a reaction by providing an alternate reaction pathway with a lower activation energy.

Question 11

Explain how an increase in concentration/pressure affects the rate of reaction.

Answer 11

• Number of particles per given volume increases
• Increased number of frequent (successful collisions)
• Rate increases

Question 12

Explain how an increase in surface area affects the rate of reaction.

Answer 12

• Exposes more reactant particles
• Increased number of collisions and successful collisions per second
• Increased rate of reaction

Question 13

Explain the effect of an increase in temperature on the rate of reaction

Answer 13

• Increased energy, so KE of particles increases
• A greater proportion of the particles have the required activation energy
• More collisions per second
• Increased number of collisions result in a reaction

Question 14

What are the two major economic advantages of the use of catalysts in industry?

Answer 14

• They increase the rate of a chemical reaction meaning that more of the desired product can be made in a given time period
• Reactions can take place at lower temperatures resulting in a decrease in the energy costs to the manufacturer

Question 15

What is a heterogeneous catalyst?

Answer 15

A catalyst that is in a different phase to the reactants

Question 16

What are 3 ways of monitoring concentration changes in a reaction?

Answer 16

• Mass (loss of mass as gas released)
• Volume (of gas produced)
• Colour ( production of solid and cross)