Question

What is the standard enthalpy change for the sublimation of iodine at 25°C and 1 atm pressure, if the enthalpy of formation of solid iodine is -107.3 kJ/mol and that of gaseous iodine is 62.4 kJ/mol?

Answer 1

The standard enthalpy change for the sublimation of iodine can be calculated using the enthalpy of formation values for solid and gaseous iodine. Sublimation is the process of a solid converting directly into a gas, bypassing the liquid phase. In this case, solid iodine  I2  is converting into gaseous iodine  I2 .The standard enthalpy change for sublimation  Hsub  can be calculated using the following equation:Hsub = Hf gaseous iodine  - Hf solid iodine Given the enthalpy of formation values:Hf solid iodine  = -107.3 kJ/molHf gaseous iodine  = 62.4 kJ/molSubstitute the values into the equation:Hsub = 62.4 kJ/mol -  -107.3 kJ/mol Hsub = 62.4 kJ/mol + 107.3 kJ/molHsub = 169.7 kJ/molTherefore, the standard enthalpy change for the sublimation of iodine at 25C and 1 atm pressure is 169.7 kJ/mol.