Unit 6: Chemical Kinetics ; Topic 6.1 Collision Theory and Rates of Reactions

Question 1

What is the rate of reaction?

Answer 1

Rate of reaction is the change of concentration of reactants or
products with time (mol dm-3 s-1)

Question 2

What factors will determine rate?

Answer 2

Surface area (usually refers to solid)

Concentration or pressure (if gas)

Temperature

Catalyst

Question 3

How is the rate found?

Answer 3

Through experimentation only

Rate of decreasing reactants
−Δ[Concentration]/ Δ[time]

Rate of increasing products
Δ[Concentration]/ Δ[time

Question 4

What changes should be measured?

Answer 4

Changes in

gas or pressure, mass, color, pH, conductivity

Question 5

Why is gas collection through a syringe good for hydrogen?

Answer 5

This set up is good for hydrogen as it is
lighter than air

Question 6

What are the characteristics of gas collection – over water?

Answer 6

Not good for water soluble chemicals, Warmer water will decrease solubility

Question 7

Is the change in mass good for light gases such as hydrogen?

Answer 7

no.

Question 8

what is the change in color?

Answer 8

Colorimetry/spectrophotometry

Question 9

what does colorimetry show?

Answer 9

Absorbance and transmittance , and it Measures concentration

Question 10

What is the collision theory?

Answer 10

1) Particles must collide.
2) Particles must have enough kinetic energy to overcome electron cloud repulsion to react. 3) Particles must collide in the correct geometrical alignment (steric factor).

Question 11

“Particles must have enough kinetic energy to overcome electron cloud repulsion to react.” what is this called?

Answer 11

This is called activation energy (Ea) and is directly proportional to the temperature in Kelvin.

Question 12

What are the factors mainly affecting the collision rate?

Answer 12

concentration/ pressure and surface area

Question 13

What are the factors mainly affecting the proportion with required activation energy?

Answer 13

Temperature and catalyst

Question 14

explain concentration in the collison theory

Answer 14

increasing the concentration increases the rate at which particles collide.

Question 15

explain surface area in the collison theory

Answer 15

increasing the surface area increases the area for particles to collide therefor increasing collisions.

Question 16

explain temperature in the collison theory

Answer 16

Increasing the temperature increases to some degree the collision rate but more importantly, it increases the number of particles that will have sufficient activation energy to react (E>Ea).

(as the temperature increases the probability of molecules having higher energy increases)

Question 17

explain catalysts in the collison theory

Answer 17

Catalysts decrease the activation energy therefore increases the number of particles that have sufficient energy to overcome the activation energy.