4 d) equilibria

Question 1

4.22 understand that some reactions are reversible and are indicated by the symbol in equations

Answer 1

Reaction which can be reversed is called reversible reaction. It is indicated by the symbol ⇌

Question 2

4.23 describe reversible reactions such as the dehydration of hydrated copper(II) sulfate and the effect of heat on ammonium chloride

Answer 2

Heating copper(II) sulphate crystals:

If you heat blue copper(II) sulphate gently, the blue crystals turn to a white powder and water is driven off. Heating causes the crystals to lose their water of crystallisation and white anhydrous copper(II) sulphate is formed.

CuSO4 . 5H2O(s) ==> CuSO4(s) + 5H2O(l)

Now if you add water to the white solid, it will turn blue and will get warm.

CuSO4(s) + 5H2O(l) ==> CuSO4 . 5H2O(s)

Heating ammonium chloride:

If you heat ammonium chloride, the white crystals disappear from the bottom of the tube and reappear further up. Heating ammonium chloride splits it into the colourless gases ammonia and hydrogen chloride.

NH4Cl(s) ==> NH3(g) + HCl(g)

These gases recombine when the condition are changed from hot to cool.

NH3(g) +HCl(g) ==> NH4Cl(s)

Question 3

4.24 understand the concept of dynamic equilibrium

Answer 3

Dynamic equilibrium is when a reversible reaction is happening both ways at the same time, at the same rate.

Question 4

4.25 predict the effects of changing the pressure and temperature on the equilibrium position in reversible reaction

Answer 4

Le Chatelier’s Principle:
- When a reversible reaction is in equilibrium and you make a change, it will do what it can to oppose that change.

The effect of pressure:

• If you increase the pressure, the equilibrium will move to reduce it again by producing fewer molecules. If you lower the pressure, the equilibrium will move to increase it again by producing more molecules.

The effect of temperature:

• If you decrease the temperature, the equilibrium will move to produce more heat to counteract the change you have made.
• If you increase the temperature, the equilibrium will move to lower it again by favouring the endothermic change.