CH9: Kinetics

Question 1

What is activation energy?

Answer 1

Min amount of KE particles need to react
- need this much energy to beak the bonds to start reaction

Question 2

What is a succcesful collision?

Answer 2

• collide in right direction facing each other
• collide with min amount of Kinetic energy

Question 3

What factors does the rate of chemical reaction depend on?

Answer 3

Collision FREQUENCY
Collision ENERGY
ACTIVATION ENERY

Question 4

How can rate of reaction be increased ?

Answer 4

INCREASING CONC- more particles available in same space - more frequent SUCCESSFUL collisions
INCREASING PRESSURE - more particles per unit volume - more frequent SUCCESSFUL collisions
INCREASING TEMP- increase KE - more frequent SUCCESSFUL collisions
A greater proportion of molecules have kinetic energy greater than activation energy
So greater proportion of collision result in reaction
Also collide with MORE ENERGY
INCREASE SA- more particles available in same amount of space - more frequent SUCCESSFUL collisions

Question 5

What is reaction rate?

Answer 5

The change in amount of reactant/product per unit time

Question 6

Rate of reaction equation?

Answer 6

Amount of reactant used/product formed / time

Question 7

Effect of catalysts ?

Answer 7

Increases rate at which reaction reaches equilibrium
- provides alternative reaction pathway with lower activation energy , so greater proportion of collisions result in a reaction

• not used up

Question 8

What is a heterogeneous catalyst? What are the effects of increasing SA of catalyst ?

Answer 8

One that is in a different phase from the other reactants e.g in different state

• reaction occurs on SURFACE of catalyst so increasing SA of catalyst = increase rate of reaction

Question 9

How do solid heterogenous catalysts work?

Answer 9

Provide a surface for a reaction to take place on

1. Reactant molecules arrive at surface/bond with solid catalyst = ADSORPTION
2. Bonds between reactant’s atoms are weakened/break up - form RADICALS which get tgt and form new molecules
3. The new molecules are detached from the catalyst = DESORPTION

Question 10

What are homogenous catalysts ? How do they work?

Answer 10

Catalysts that are in same physical state as reactants

• during homogenous catalysis, reactants combine with catalysts to make INTERMEDIATE species
• this reacts to form products and reform the catalyst

Question 11

What is a Maxwell-Boltzmann distribution curve ? How does temperature and catalysts affect the curve ?

Answer 11

Graph that shows the distribution of energies at a certain temp
- only a small proportion of molecules in the sample have enough energy for an effective collision

INCREASE TEMP : particles gain KE
- meaning a higher proportion of particles have KE > Ea to cause chemical reaction
CURVE FLATTENS /PEAK SHIFTS RIGHT

CATALYST : Provides another pathway with lower activation energy
- by lowering activation energy - greater proportion of molecules have activation energy
ACTIVATION ENERGY MOVES DOWN ON GRAPH