Heat of Neutralisation

Question 1

What is neutralisation?

Answer 1

Neutralisation is the reaction between an acid and a base to form a salt and water

Question 2

Are neutralisation reactions nearly always exothermic or endothermic?

Answer 2

They are nearly always exothermic

Question 3

Define heat of neutralisation.

Answer 3

Heat of neutralisation is the heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base

Question 4

When is the term heat of neutralisation used?

Answer 4

It is used when discussing heat changes involved in neutralisation reactions

Question 5

What is heat of neutralisation measured in?

Answer 5

kj mol-1

Question 6

Why are the heat of neutralisation values almost the same between all reactions involving a strong acid and a strong base?
(2)

Answer 6

The essential reaction occurring is the same in all cases

The reaction that occurs simply involved a proton and a hydroxide ion coming together to form water

Question 7

What can be noted in relation to the heat of neutralisation value that results from a reaction involving a weak acid or weak base?

Answer 7

The heat of neutralisation value is less than -57 kj mol-1

Question 8

Why is the heat of neutralisation value always below -57 kj mol-1 when the reaction involves a weak acid or weak base?
(4)

Answer 8

This is because weak acids and weak bases are not fully dissociated in water

Fir complete neutralisation to occur and form one mole of water, the weak acid or base must become fully dissociated

This dissociation requires energy i.e. it is endothermic

Therefore, the heat released will be less than 57 kj since a certain quantity is required to cause complete dissociation of the acid or base