Solution
= Solution
The \b[<standard enthalpy of formation>] is the <enthalpy> change on forming exactly one <mole> of the specified compound in its stated <standard state> from its constituent <chemical elements> in their reference states at the same specified <temperature>. The reference states are normally the stable elemental forms at the standard <pressure>. A <standard state> does not itself mean 298 K; <temperature> must be stated separately.