Rate of reaction and equilibrium

Question 1

Definition of rate of reaction

Answer 1

The change in concentration of a reactant or product over time

Question 2

How is rate calculated?

Answer 2

rate = change in concentration/change in time

Question 3

Which collisions lead to a reaction?

Answer 3

Those which have the correct orientation and sufficient energy to overcome the activation energy

Question 4

How does increased concentration affect rate of reaction?

Answer 4

Number of particles in same volume is increased so more frequent successful collisions so rate increases

Question 5

How does increased pressure affect rate of reaction?

Answer 5

Concentration of gas molecules increases as same number of molecules occupy a smaller space –> more frequent successful collisions so rate increases

Question 6

How does increased temperature affect rate of reaction?

Answer 6

Increases kinetic energy of particles so more particles have energy equal to or greater than the activation energy –> more frequent successful collisions

Question 7

How does temperature affect a Boltzmam curve?

Answer 7

• With a higher temp, curve shifts RIGHT and DOWN
• Total area under curve is the same (no. particles)
• Must be labelled (higher temp, lower temp)

Question 8

How does adding a catalyst affect a Boltzman curve?

Answer 8

Moves Ea back so area under curve after Ec (with catalyst) is bigger than without using a catalyst. Therefore more particles have E > Ea so more frequent successful collisions occur

Question 9

Definition of a catalyst

Answer 9

A substance that provides an alternative reaction pathway of lower activation energy

Question 10

What are homogeneous and heterogeneous catalysts?

Answer 10

Homo - same physical states as reactants

Hetero - different physical states to reactants (usually solid)

Question 11

How are catalysts not used up?

Answer 11

Used in one reaction and regenerated in a later reaction

e. g.
1. A + B –> D
2. D –> B + E

Question 12

What are the 2 benefits of catalysts?

Answer 12

Cost: allows lower temperatures and pressures to be used –> reduces energy demand which reduces cost
Environment: reduces fossil fuel consumption –> less greenhouse gas emissions

Question 13

What are the required conditions to reach dynamic equilibrium?

Answer 13

1. Rate of forward reaction = rate of reverse reaction
2. Conc. of reactants and products stays the same
3. Closed system

Question 14

How can you tell when dynamic equilibrium has been reached on a conc/time graph?

Answer 14

When both lines remain constant

Question 15

How does a graph show where equilibrium lies?

Answer 15

More products = equilibrium lies to the right

More reactants = equilibrium lies to the left

Question 16

What is Le Chatelier’s Principle?

Answer 16

When a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change

Question 17

What effect does increasing the concentration of reactants have on equilibrium?

Answer 17

Equilibrium shifts to the right to use up the added reactants so the yield of products increases

Question 18

How does increasing the pressure of reactants affect equilibrium?

Answer 18

Equilibrium shifts to the side with the fewest moles to minimise the change, which is right

Question 19

What happens when pressure is changed but there are the same amount of moles on both sides?

Answer 19

No shift in equilibriums position