Which of the following is/are endothermic reaction(s)? — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

Let's analyze each reaction:<br>(a) Combustion of methane ($CH_4$ + 2$O_2$ → $CO_2$ + 2$H_2O$) is highly exothermic (ΔH < 0).<br>(b) Decomposition of water (2$H_2O$ → 2$H_2$ + $O_2$) is the reverse of water formation, which is highly exothermic. Therefore, decomposition is endothermic (ΔH > 0).<br>(c) Dehydrogenation of ethane to ethylene ($C_2H_6$ → $C_2H_4$ + $H_2$) requires breaking C-H bonds without forming sufficiently stronger bonds, making it an endothermic process (ΔH > 0).<br>(d) Conversion of graphite to diamond (C_graphite → C_diamond) is endothermic (ΔH = +1.9 kJ/mol) as diamond is a higher energy allotrope.<br>Therefore, the correct options are B, C, and D.