According to standard IUPAC conventions in thermochemistry, the standard enthalpy of formation () at — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

The standard enthalpy of formation ($\Delta_f H^\circ$) is arbitrarily assigned a value of zero for pure elements residing in their most stable and abundant reference states at 1 bar and specified temperature. Graphite is more stable than diamond, so $\Delta_f H^\circ(C_{graphite}) = 0$. Rhombic sulphur is the stable polymorph at room temperature, making $\Delta_f H^\circ(S_{rhombic}) = 0$. For phosphorus, the highly reactive white allotrope is the accepted standard reference, meaning $\Delta_f H^\circ(P_{white}) = 0$.