In the context of enthalpy of formation, what does the difference between the enthalpies of the products and the reactants represent?

• A. The entropy change of the reaction (ΔS)
• B. The equilibrium constant of the reaction (K)
• C. The activation energy of the reaction
• D. The standard enthalpy change of the reaction (ΔH)

Answer: (D)

Verified step by step guidance

1. Understand that the enthalpy of formation refers to the change in enthalpy when one mole of a compound is formed from its elements in their standard states.
2. Recall that the enthalpy change of a reaction (ΔH) can be calculated by subtracting the sum of the enthalpies of the reactants from the sum of the enthalpies of the products, expressed as: \(\Delta H = \sum \Delta H_{\text{products}} - \sum \Delta H_{\text{reactants}}\).
3. Recognize that this difference represents the overall heat absorbed or released during the reaction under standard conditions, which is the standard enthalpy change of the reaction.
4. Note that this value is distinct from entropy change (ΔS), equilibrium constant (K), or activation energy, which describe different thermodynamic or kinetic properties of the reaction.
5. Therefore, the difference between the enthalpies of the products and reactants directly corresponds to the standard enthalpy change of the reaction (ΔH).