Chemical Equilibria

Question 1

Dynamic equilibrium?

Answer 1

Rate of forward reaction = Rate of backward reaction for reversible reaction such that there is no net change in concentration of reactants and products

Question 2

Kc expression?

One thing to note about value of K.

Answer 2

Refer to image 1

Only temperature affects value of K

Question 3

Kp expression?

Answer 3

Refer to image 2

Question 4

Kc/Kp for heterogeneous equation

Answer 4

x Pure solid (s)
x Pure Liquid (l)
–> = density, constant

x Solvent (Water) –> Large amount, constant

Question 5

Solving equilibrium problem (Calculations involving Kc)

Answer 5

1. Balanced chemical Equation
2. ICE table (Moles/Partial pressure)
   - Initial amount
   - Change in amount [Follows mole ratio]
   - Equilbrium amount
   - -> If moles, rmb convert to concentration (divide by V)
3. Check homo/hetrogenous. Write Kc expression.
4. Sub in calculate equilibrium concentration/partial pressure into Kc expression

Question 6

Useful things to note when solving equilibrium problems

Answer 6

• Initially, no product formed
• Let volume be V
• For pressure qn, ‘Total pressure’ = Pressure at eqm

Question 7

Converting between eqm moles and partial pressure

Answer 7

Pa = na/ntotal x ptotal

Question 8

Le Chatelier’s Principle

Factors affecting position of equilibrium

Answer 8

If a change occurs in one of the condictions (Concentration,Pressure,Temperature) when reversible reaction is in dynamic equilbrium, position of equilibrium shifts to minimise change.

Question 9

Answering qns involving factors affecting position of equilibrium

Answer 9

1. Impact of change in conditions
2. Position of equilibrium
3. Purpose
4. Yield/ Composition

Question 10

Changing concentration on position of equilibrium

Answer 10

Refer to image 3

Question 11

Effect of adding water into aqueous equilibrium system

Answer 11

• Decrease concentration of all aqueous ions

- Eqm position shift to (side with more ions) to produce more ions

Question 12

Changing pressure (Gaseous reaction) on position of equilibrium

Answer 12

Refer to image 4

Question 13

Adding inert gas at constant volume

Answer 13

No effect on position of equilirium

• No change in partial pressure of reactants/products

Question 14

Adding inert gas at constant pressure

Answer 14

Equilibrium shift to (side with more moles of gaseous molecules) to increase pressure

• Total volume increase, decrease partial pressure of reactants/products

Question 15

Changing temperature on position of equilibrium

Answer 15

Refer to image 5

Question 16

Effect of catalyst

Answer 16

Equilibrium established faster

Question 17

Relationship between K and spontaneity of reaction

Answer 17

Refer to image 6,7

Question 18

Relationship between standard Gibbs free energy and position of equilibrium

Answer 18

Refer to image 8