Unit 4 - Lesson 5: Reversible Reactions

Question 1

What’s a reversible reaction?

Answer 1

A reaction that can work in both directions (reactants can form products and those products can react to form the reactants).

Question 2

What symbol in an equation indicates that the reaction is reversible?

Answer 2

⇌

Question 3

What are two examples of reversible reactions that you need to memorise for the exam?

Answer 3

Thermal decomposition of ammonium chloride
AND
Hydration of copper (II) sulfate

Question 4

Answer these questions about the thermal decomposition of ammonium chloride:
1. When you heat ammonium chloride, what does it split into?
2. If you cool the products that are produced after heating ammonium chloride, what is produced?
3. What can thermal decomposition of ammonium chloride be used to demonstrate?

Answer 4

1. Heating ammonium chloride splits it into hydrogen chloride gas and ammonia gas (endothermic).
2. Ammonium chloride (exothermic).
3. The diffusion of gases using a glass tubing, rubber bungs, cotton wool soaked in ammonia, cotton wool soaked in HCl and a white ring forms.

Question 5

Answer these questions about the hydration of copper (II) sulfate:
1. When you add water to anhydrous copper (II) sulfate, what is made?
2. Once hydrated, what colour does the copper (II) sulfate turn?
3. Are reversible reactions always endothermic or exothermic or BOTH?
4. What does the colour change help with?

Answer 5

1. Hydrated copper (II) sulfate. CUSO4 (s) + 4H2O (l) ⇌ CuSO4.5H2O (s)
2. Hydrated copper (II) sulfate turns from a white powder to blue crystals.
3. Reversible reactions are always endothermic in one direction and exothermic in the other.
4. The colour change helps recognise when reactions are complete.