Equilibrium

Question 1

Key points in a dynamic equilibrium

Answer 1

Rate of forward reaction = rate of back reaction
Concentration of products/reactants don’t change
Must be in a closed system

Question 2

State Le Chatelier’s Principle

Answer 2

System in equilibrium will counter any external changes to minimize the effect of the change

Question 3

Position of equilibrium

Answer 3

Indicates extent of reaction and which reaction is favoured

Question 4

What happens to the P of E when the pressure/conc changes?

Answer 4

P of E changes temporarily

Question 5

What happens to the P of E when the temperature changes?

Answer 5

P of E changes permanently

Question 6

Homogenous

Answer 6

All species in same state

Question 7

Heterogenous

Answer 7

All species in different states

Question 8

What do you omit in heterogenous equilibria and why

Answer 8

S and L

Not concentrations

Question 9

What is Kc?

Answer 9

Numerical value of the P of E

Question 10

Kc<1

Answer 10

P of E closer to reactants

Question 11

Kc>1

Answer 11

P of E closer to products

Question 12

Kc=1

Answer 12

P of E is halfway

Question 13

How to use units

Answer 13

Cross out the same no of mol dm-3 from the top and bottom

Count the no of mols and no of dm-3 and add them

Question 14

How to calculate equilibrium concentrations

Answer 14

Use given equation and work out equilibrium amounts of all species
Write Kc expression, sub in values and calculate Kc

Question 15

What is Kp

Answer 15

When equilibria involve gases
Equilibrium constants are in terms of partial pressures
Conc and pressure are proportional, Kc and Kp are related

Question 16

How to calculate Kp (homogeneous)

Answer 16

Find mole fractions of gases involved
Find partial pressure
Use equation to calculate Kp

Question 17

How to calculate mole fractions

Answer 17

Gas moles/ total no of gas moles

All mole fraction results should add up to 1

Question 18

How to calculate partial pressures

Answer 18

Mole fraction/total pressure at equilibrium

Question 19

How to calculate Kp (heterogenous)

Answer 19

Do the same but omit S and L

Question 20

What factors affect Kp and Kc

Answer 20

Only a change in temperature affects Kc/Kp

Pressure has no impact on either constant

Question 21

What happens when the temperature changes

Answer 21

System is no longer in equilibrium
Ratios between reactants and products are no longer Kc/Kp
Partial pressures/concs change to give new values
P of E changes to oppose temperature change
New equilibrium reached, Kc/Kp equal to new value

Question 22

What happens when the concentration changes

Answer 22

Kc and Kp will initially change but concs/pressures will change back

Question 23

Catalysts

Answer 23

Decreases time taken for a system to reach equilibrium, increase R of R
Does not affect P of E