10.4 Dynamic Equilibrium And Le Chatliers Principle

Question 1

Reversible reactions

Answer 1

Take place in forward and reverse directions

Question 2

What happens during dynamic equilibrium?

Answer 2

Rate of forward reactions is equal to the rate of backward reactions
Concentrations of reactants and products do not change

Question 3

Closed system

Answer 3

Isolated from surroundings, temperature, pressure, concentration are unaffected by outside influences

Question 4

Le Chatlier’s principle

Answer 4

When a system in equilibrium is subjected to an external change, system readjusts to minimise the effect of that change

Question 5

Requirement in order for reaction to stay in equilibrium

Answer 5

System must be closed

Question 6

If equilibrium position has shifted to the right….

Answer 6

More products are formed

Question 7

If equilibrium position has shifted to the left….

Answer 7

More reactants are formed

Question 8

Changes to equilibrium with concentration

Answer 8

Add solution of yellow potassium dichromate to a beaker
Add dilute sulfuric acid dropwise until there is no further change - changes to orange colour
Add aqueous sodium hydroxide until no further change, colour changes back to yellow

Question 9

How does concentration affect position of equilibrium?

Answer 9

When adding sulfuric acid, concentration of H+ ions is increased, which increases rate of forward reactions
Equilibrium shifts towards the right, so more products are formed and solution turns orange

Question 10

Concentration and equilibrium

Answer 10

As concentration of substance is increased, position of equilibrium moves away from that substance

Question 11

Temperature and equilibrium

Answer 11

Increase in temperature - equilibrium position shifts in endothermic direction
Decrease in temperature - equilibrium position shifts in exothermic direction

Question 12

Chromate ions and dichromate ions colour in solution

Answer 12

Chromate - yellow

Dichromate - orange

Question 13

Experiment showing effect of temperature on equilibrium

Answer 13

Dissolve cobalt chloride in water in a boiling tube - add a small quantity of HCl and place in iced water (pink solution)
Transfer boiling tube into boiling water in water bath - solution turns blue colour
When back in ice water, turns back into pink

Question 14

How does this experiment show relationship between equilibrium and temperature?

Answer 14

When temperature is decreased, there are more backward reactions (exothermic), so the pink solution is formed
When temperature is increased, there are more forward reactions (endothermic), so blue solution is formed

Question 15

Effect of pressure on equilibrium position

Answer 15

Increasing pressure means equilibrium position shifts towards the side with fewer mols

Question 16

Experiment to show effect of pressure on equilibrium position

Answer 16

NO2 is a brown gas, N2O4 is colourless
2NO2 >< N2O4
Increase pressure, moves to side with fewer mols, so more N2O4 is formed, change from brown to colourless

Question 17

Effect of catalyst on equilibrium

Answer 17

Catalyst doesn’t change position of equilibrium

Speeds up rate of both forward and backward reactions

Question 18

Making ammonia with Haber process

Answer 18

N2 + 3H2 >< 2NH3
ΔH = -92KJ/mol
Low temperature and high pressure will increase yield
Low temperature, low reaction rate - so compromise temperature used
High pressure - not safe, risk of explosion, requires strong container and a lot of energy, so compromise pressure is used

Question 19

Conditions for Haber process

Answer 19

350-500oC temperature
100-200 atm pressure
Iron catalyst