Answer to Question #43217 in Physical Chemistry for Sumit

Question

Justify - H*(CO2) = Delta_f H*(CO2) [*means zero in superscript and _f means f in subscript]

where, H* is standard enthalpy and Delta_f H* means standard enthalpy change of formation.

Answer 1

C + O₂ --> CO₂

Delta_f H*(CO₂) = H*(CO₂) - [H*(C) + H*(O₂)]
The standard enthalpy of elementary substance is zero:
H*(C) = H*(O₂) = 0
Therefore
Delta_f H*(CO₂) = H*(CO₂) - [H*(C) + H*(O₂)] = H*(CO₂) - [0 + 0] = H*(CO₂)