Topic 9 - Kinetics I

Question 1

What is the Collision Theory

Answer 1

a reaction won’t take place unless
1. two particles are correctly orientated
2. two particles collide with a certain minimum amount of kinetic energy

Question 2

What is activation energy

Answer 2

the minimum amount of energy particles need to react

Question 3

What are the axes of a Maxwell-Boltzmann Distribution curve

Answer 3

y = n.o of molecules
x = energy

Question 4

What does a Maxwell-Boltzmann Distribution curve look like

Answer 4

1. starts at (0,0) because no molecules have zero energy
2. peak = most probable energy
3. mean energy = to the right of peak
4. shaded area on right = molecules that have at least activation energy

Question 5

What affect does increasing temp have on Maxwell-Boltzmann Distribution curve

Answer 5

more particles on average have at least activation energy
- entire curve shifts right
- area stays same as total n.o molecules is same

Question 6

Why does increasing temp speed up rate of reaction

Answer 6

particles moving faster = more likely to collide more often

Question 7

What affect does using a catalyst have on Maxwell-Boltzmann Distribution curve

Answer 7

activation energy is lower
more particles have at least Ea.

Question 8

How does increasing concentration speed up rate of reaction

Answer 8

more particles in a given volume = collide more frequently = more chance

Question 9

How does increasing pressure speed up rate of reaction

Answer 9

gases only = more particles in given volume = higher frequency of successful collisions

Question 10

How does a catalyst speed up the rate of reaction

Answer 10

provides an alternative reaction pathway with a lower activation energy

Question 11

What is reaction rate

Answer 11

change in amount of reactant or product per unit time

Question 12

What is a heterogeneous catalyst

Answer 12

in a different phase from reactants

Question 13

How does heterogeneous catalysis work

Answer 13

• reactants diffuse onto the surface of catalyst
• adsorption takes place = bonds for between catalyst & reactants, strong enough to break covalent bonds in reactants, weak enough to eventually break
• reaction takes places on surface of catalyst
• desorption takes place = bonds with catalyst have weakened/broken, product diffuses away from catalyst

Question 14

What does the reaction profile with a homogeneous catalyst look like ?

Answer 14

height of curve with activation energy is lower (one peak)

Question 15

What is homogeneous catalyst

Answer 15

in same phase as reactants

Question 16

How does homogeneous catalysis work

Answer 16

reactants combine with aqueous catalyst to make an intermediate species, which then reacts to form products and reform catalyst

Question 17

What does the reaction profile look like for homogeneous catalysis

Answer 17

• one high peal becomes 2 smaller ones
• intermediate where dips between 2 small peaks