Reversible Reactions

Question 1

What is a reversible reaction?

Answer 1

• When the products of a reaction can react to form the original reactants.

Question 2

How can the direction of reversible reactions be changed?

Give an example of a reversible reaction that you could change the conditions of to change the direction of the reaction.

Answer 2

• Direction of reversible reactions can be changed by changing the conditions.
• ammonium chloride —–heat —–> ammonia + hydrogen chloride.
• Ammonia + hydrogen chloride –cool –> ammonium chloride.

Question 3

What is the general rule for energy transferred in reversible reactions?

Give an example of a reversible reaction that follows this general rule

Answer 3

• If a reversible reaction is exothermic in one direction, it will be endothermic in the other direction.
• The same amount of energy is transferred in each case.

E.g. Hydrated copper sulphate (blue) –endothermic-> anhydrous copper sulphate (white) + water

Anydrous copper sulphate (white) + water –exothermic–> hydrated copper suphate (blue)

Question 4

When is equilibrium reached in a reversible reaction?

Answer 4

• When the reaction is occurring in aparatus that prevents the escape of reactants/ products (closed system.)
• Therefore, the forward and reverse reactions occur at exactly the same rate (as concentrations of reactants/ products are the same.)

Question 5

What is Le Chartelier’s principle?

Answer 5

• If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change.

Question 6

What happens to the reversible reaction if the concentration of either products/ reactants is changed?

Answer 6

• The system is no longer at equilibrium/ the concentrations of all the substances will change until equilibrium is reached again.

Question 7

What happens if we increase the concentration of a reactant?

Answer 7

• More products will be formed until equilibrium is reached again.

Question 8

What happens if we decrease the concentration of the product?

Answer 8

• More reactants will react until equilibrium is reached again.

Question 9

What happens if the temperature of a system is increased at equilibrium?

TO THE AMOUNT OF PRODUCTS

Answer 9

• The relative amount of products at equilibrium increases for an endothermic reaction.
• The relative amount of products at equilibrium decreases for an
  exothermic reaction.

Question 10

What happens if the temperature of a system is decreased at equilibrium?

TO THE AMOUNT OF PRODUCTS

Answer 10

• The relative amount of products at equilibrium decreases for an
  endothermic reaction.
• The relative amount of products at equilibrium increases for an
  exothermic reaction.

Question 11

What happens when a gaseous reaction system (at equilibrium) increases in pressure?

Answer 11

• The equilibrium position will shift towards the side with a smaller number of molecules.

Question 12

What happens when a gaseous reaction system (at equilibrium) decreases in pressure?

Answer 12

• A decrease in pressure causes the equilibrium position to shift
  towards the side with the larger number of molecules.