A quantity that cannot be directly measured is — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

Methane ($CH_4$) cannot be synthesized directly from carbon (graphite) and hydrogen gas because the reaction does not go cleanly to completion; other hydrocarbons (like ethane, ethylene, and acetylene) are formed simultaneously. Thus, the heat of formation of methane cannot be measured directly and must be determined indirectly using Hess's Law of constant heat summation.