The standard enthalpy of formation of a substance — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

The standard enthalpy of formation of a substance can be positive (endothermic formation, like $O_3$ or $NO$), negative (exothermic formation, like $H_2O$ or $CO_2$), or zero (for elements in their standard states like $O_2$(g) and C(graphite)).