1.5 Kinetics

Question 1

What is the definition of Rate of Reaction?

Answer 1

Measure of the change of the concentration of products or reactants over time

Question 2

What is the definition of collision theory?

Answer 2

That for a reaction to take place two particles must collide with enough energy to break the bonds

Question 3

Why do collisions often not result in reactions?

Answer 3

• Not enough energy
• Wrong orientation of molecules

Question 4

What factors affect the rate of reaction and why?

Answer 4

Increasing temperature- Increases speed of the molecules so increases collisions
Increasing concentration- More particles in same volume
Increasing pressure- PArticles are closer together
Increasing surface area- More surfaces available for reaction

Question 5

In what ways can rate be measured?

Answer 5

• Time taken for precipitate to form (disappearing cross)
• Volume of gas produced over time
• Mass change overtime

Question 6

What is the Maxwell Boltzmann distribution?

Answer 6

The distribution of energy amongst particles

Question 7

Why does the Maxwell-Boltzmann graph start at the origin?

Answer 7

No particles have zero energy

Question 8

What does the area under the graph in the Maxwell Boltzmann distribution show?

Answer 8

The total number of particles

Question 9

What is the definition of activation energy?

Answer 9

The minimum amount of energy required for a reaction to take place

Question 10

What is the difference between average energy and most probable energy on a Maxwell Boltzmann graph?

Answer 10

Average energy is the mean energy of the particles and is around the middle of the x axis and most probable is the energy at the peak with the most particles

Question 11

Why do exothermic reactions not spontaneously occur in room temperature?

Answer 11

Activation Energy

Question 12

What is the effect of temperature on the reaction curve?

Answer 12

• Lower and moves to right
• Number of particles with very high energy increases
• Area under the curve remains the same

Question 13

What is the effect of high concentration on the reaction curve?

Answer 13

• Curve is higher and move to the right

Question 14

Why does the reaction curve plateau?

Answer 14

Limiting reactant has run out so the rate is at zero

Question 15

Why do some particles have very low energies?

Answer 15

Collisions cause molecules to lose energy

Question 16

What is the definition of a catalyst?

Answer 16

Substances that affect the rate of reactions without being chemically changed

Question 17

How do catalysts work?

Answer 17

Provide a different pathway with a lower activation energy
Means more particles are at a high enough energy to react

Question 18

What is a catalytic converter used for?

Answer 18

To reduce number of polluting gases produced by cars

Question 19

How do catalytic converters work and give equations?

Answer 19

• Large surface area with honeycomb shape made of ceramic and coated with platinum less of the expensive metals needed
  CO+NO2 —> N + CO2
  CxHx + NO —> N + CO2 + H2O

Question 20

How do catalytic conversion reactions work?

Answer 20

1. Adsorption- gases form weak bonds with metal atoms holding gases in right position to react
2. Desorption- Products break away from metal atoms freeing up catalyst surface

Question 21

Why is the strength of bonds critical in catalytic conversion?

Answer 21

• Strong enough to hold gases in place
• Weak enough to easily release products

Question 22

Why is a honeycomb/ powder structure used in catalysts?

Answer 22

• Greater surface area
• More successful collisions as more reactant surface is exposed
• Rate increases without need for high pressures/temperature