OnlineCBT
Chemistry · THERMODYNAMICS
हिन्दीConsider the following chemical reactions: (A) \( \text{H}_2(g) + \frac{1}{2}\text{O}_2(g) \to \text{H}_2\text{O}(l) \) (B) \( \text{C}(\text{graphite}) + 2\text{H}_2(g) \to \text{CH}_4(g) \) (C) \( \text{CaO}(s) + \text{CO}_2(g) \to \text{CaCO}_3(s) \) (D) \( \text{H}_2(g) + \text{Br}_2(l) \to 2\text{HBr}(g) \) In how many of the above reactions does the reaction enthalpy (\( \Delta_r H^\ominus \)) directly represent the standard molar enthalpy of formation (\( \Delta_f H^\ominus \)) of the product? Which of the above statements is/are correct?
Correct answer · Option 2
Only two
Explanation
Only reactions (A) and (B) form 1 mole of compound from their constituent elements in reference states. Reaction (C) involves compounds as reactants, and reaction (D) forms 2 moles of HBr instead of 1 mole. Thus, exactly two reactions qualify.
