Module 3: Chemical Equilibrium IPS (3.2.3)

Question 1

Dynamic Equilibrium

Answer 1

1. Rate of forward reaction = rate of reverse reaction.
2. Concentration of reactants& products DO NOT CHANGE.
3. Closed system: Isolated from its surrounding, to remain in equilibrium.

Question 2

Le Chatelier’s Principle

Answer 2

1. When a system in equilibrium is subjected to an external change, the system readjusts itself to minimise its’ effect.

Question 3

Concentration

Answer 3

1. INCREASE REACTANTS ——-> Shifts right.
2. DECREASE REACTANTS ——-> Shifts left.
   • INVESTIGATION
3. Add solution of K₂CrO₄ to beaker.
4. Add dilute H₂SO₄ drop wise until no further change. Orange colour present.
5. Add aqueous NaOH until no further change. Yellow colour present.
6. Adding H⁺ ions increases rate of forward reaction so eqm shifts right, turning orange.
7. Adding NaOH reacts with H⁺, decreasing H⁺ concentration, eqm shifts right, turning yellow.
8. CrO₄²⁻ (aq) + 2H⁺(aq) ⇌ Cr₂O₇²⁻(aq)- + H₂O (l)
9. Chromate ions are yellow and dichromate ions are orange.

Question 4

Temperature

Answer 4

1. INCREASE °C shifts eqm to endothermic ΔH +
2. DECREASE °C shifts eqm to exothermic ΔH -
   •INVESTIGATION
3. Dissolve CoCl4 in boiling tube, add small amount of dilute HCl and place in ice water. Pink colour present.
4. Set up hot water bath and place boiling tube in. Solution turns blue.
5. Forward reaction is endothermic, shifts right to take heat energy in and minimise increase in °C.
6. [Co(H₂O)₆]²⁺(aq) +4Cl⁻ ⇌ CoCl₄²⁻ (aq) + 6H₂O (l)

Question 5

Pressure

Answer 5

1. Pressure of a gas is proportional to its concentration.
2. INCREASING pressure shifts eqm to side with fewer moles to reduce the pressure of the system.
3. DECREASING pressure shifts eqm to side with more moles.

Question 6

Catalyst

Answer 6

1. Does NOT affect equilibrium but speeds up rate of forward and reverse equally.
2. Allows equilibrium to be reached faster.