Question

For which one of the following is the enthalpy of the reaction the same as the enthalpy of formation?

A) H₂ (g) + F₂ (g) → 2 HF (g)
B) Ca (s) + ½ O₂ (g) → CaO (s)
C) 2 CH₃OH (l) + 3 O₂ (g) → 2 CO₂ (g) + 4 H₂O(g)
D) SrO (s) + CO₂ (g) → SrCO₃ (s)

Answer 1

Option B, the reaction forming CaO from elemental calcium and oxygen, is the one where the enthalpy of the reaction is equal to the enthalpy of formation.

Step-by-step explanation:

The enthalpy of the reaction is the same as the enthalpy of formation for a reaction where a compound is formed from its elements in their standard states. Among the given options, the enthalpy of reaction for option B, which is the reaction Ca (s) + ½ O₂ (g) → CaO (s), corresponds to the standard enthalpy of formation of calcium oxide (CaO). This is because it represents the formation of a compound from its constituent elements in their standard states, which by definition is what an enthalpy of formation represents.