Heat of Sublimation

Calculate the enthalpy of sublimation of Iodine from the following data:

H2(g) + I2(s) à 2 HI(g)      DHR = 51.9 kJ

H2(g) + I2(g) à 2 HI(g)      DHR = -9.2 kJ

Calculations:

H2(g) + I2(s) à 2 HI(g) -- I      DHR = 51.9 kJ

H2(g) + I2(g) à 2 HI(g) -- II      DHR = -9.2 kJ

From Hess's law of constant heat of summation,

Subtracting equation II from I gives,

I2(s) - I2(g) = 0      DHR = 51.9 - (-9.2) = 61.1 kJ

i.e.,

I2(s) à I2(g)      DHR = 61.1 kJ

That is enthalpy of sublimation (transformation of iodine from solid phase to directly vapor phase) of iodine is 61.1 kJ