In the industrial production of sulphuric acid, SO3 is carefully reacted with water:
SO3 + H2O → H2SO4
any excess SO3 giving rise to what is called oleum, a solution of SO3 in sulphuric acid. The relationship between the freezing point (f.p.) of sulphuric acid and the presence of small amounts of dissolved SO3 is as below:
|
|
Pure H2SO4
|
1 mol% SO3
|
2 mol% SO3
|
3 mol% SO3
|
|
Tfp /°C
|
10.36
|
9.74
|
9.12
|
8.50
|
Assume that SO3 in H2SO4 forms a solution without reaction. Graphically or otherwise, estimate the enthalpy of fusion of sulphuric acid (note that 1 mole % corresponds to a mole fraction of 0.01).