TERMOKIMIA -HEAT OF REACTION

Method of Calculating ΔH

a) Quantity of heat change in a substance depends on (kuantiti perubahan haba bg sesuatu bahan bergantung kepada):

i- Mass of substance (m in grams)

ii- Specific heat capacity of a substance (c in Jg-1 oC-1)

iii- Temperature change (θ in oC)

b) As chemical reaction occurs in an aqueous solution, assumptions are made during the calculation of heat of reaction :

Density of aq solution = Density of water = 1 g cm-3

Density of aq solution = Density of water = 1 g cm-3

Example :

- 1 cm3 of aq solution has a mass of 1 g

- 2 cm3 of aq solution has a mass of 2g

Specific heat capacity of solution = Specific heat capacity of water = 4.2 Jg-1 oC-1

The heat of reaction can be calculated by using formula

Energy change, H = mcθ

Four type of heat of reaction :

1) Heat of precipitation - Heat of precipitation is heat change when 1 mole of precipitate is formed from its ions.

2) Heat of displacement- Heat of displacement is heat change when 1 mole of metal is displaced from its ionic solution by a more electropositive metal.

3) Heat of neutralisation - Heat of neutralization is heat energy released when 1 mole of water is formed from neutralization between one mole of hydrogen ions,H⁺ from an acid and one mole of hydroxide ions, OH^- from an alkali