Question

15. The heat of formation of OsO4 (s) , Hof OsO4 (s) , is -391 kJ mole-1 at 298 K and the heat of sublimation is 56.4 kJ mole-1. What is Ho298 for the process shown below under standard state conditions? Os (s) + 2 O2(g) -----> OsO4 (g)

Answer 1

Os (s) + 2O₂ (g) → OsO₄ (g)

Heat of formation H = -391 Kj/mole

T = 298K

Heat of sublimation H sub = 56.4 Kj/mole

Sublimation is a process in which a solid substance directly changes into its vapours at any temperature below its melting point. Enthalpy of sublimation is defined as the change in enthalpy when one mole of a solid substance is converted into its vapours without melting at a temperature below its melting point is called the enthalpy of sublimation. Sublimation is the heat absorbed by one gram or unit mass of a substance in theprocess of changing, at a constant temperature and pressure, from a solid to a gaseous state.

The heat of formation is defined as the heat evolved or absorbed when one ole of a compound is formed from its constituent atoms.