Topic 9 - Kinetics 1

Question 1

What effect does temperature have on the rate of reaction?

Answer 1

increased temp = increased rate

• increase in kinetic energy
• particles move faster ∴ frequency of collisions increase
• no. collisions with energy ≥ Ea increases

Question 2

What effect does concentration/pressure have on the rate of reaction?

Answer 2

increased conc = increased rate

• more particles ∴ frequency of collisions increase
• no. collisions with energy ≥ Ea increases

Question 3

What effect does surface area have on the rate of reaction?

Answer 3

increased SA = increased rate

• more particles exposed to collide with other reactants
• no. collisions with energy ≥ Ea increases

Question 4

What factors affect collisions?

Answer 4

• orientation (atoms must face correct way when colliding in order to react)
• activation energy (particles must collide with sufficient energy to break bonds)
• steric hinderance (large atoms attached to central atom can hinder reacting species from attacking central atom)

Question 5

rate =

Answer 5

[reactant]
________
time

Question 6

rate ∝

Answer 6

Vf -Vt
or
1/t

Question 7

What do Maxwell-Boltzmann distribution curves show?

Answer 7

number of particles at any given energy

total area under curve = total no. particles

Question 8

How does an increase in temperature affect a Maxwell-Boltzmann distribution curve?

Answer 8

shifts peak right and down

-total no. particles stays the same but more have energy ≥ Ea

Question 9

How does an increase in concentration affect a Maxwell-Boltzmann distribution curve?

Answer 9

total area under curve increases (line is higher)

-no. particles with energy ≥ Ea increases

Question 10

How does a catalyst affect a Maxwell-Boltzmann distribution curve?

Answer 10

• lower Ea

- no. particles with energy ≥ Ea increases

Question 11

How do catalysts increase the rate of reaction?

Answer 11

• reduce the activation energy

- by providing an alternative pathway to a low energy intermediate

Question 12

What is a homogeneous catalyst?

Answer 12

a catalyst in the same phase (state) as the reaction

Question 13

How does a homogeneous catalyst work?

Answer 13

• reacts with one of the reactants to form an intermediate
• intermediate reacts with the other reactant(s) to reform the catalyst

-avoids collisions between two negative particles (which would repel eachother so would need a lot of energy)

Question 14

What is a heterogeneous catalyst?

Answer 14

a catalyst in a different phase (state) to the reaction

Question 15

How does a heterogeneous catalyst work?

Answer 15

• provides an active site which reactants adsorb to (weakens bonds)
• new bonds form and adsorbed reactants are changed into adsorbed product(s)
• product(s) deadsorb, freeing the active site to be used again

Question 16

What are enzymes?

Answer 16

biological catalysts that have an active site specific to a certain substrate
-only work at a limited range of temperatures (otherwise will denature, changing the shape of the active site)