Chemistry - Thermochemistry Question with Solution | TestHub

Combustion of methane releases heat, so (a) is exothermic. Splitting water into H_₂ and O_₂ requires energy input (the reverse of highly exothermic H_₂ combustion), so (b) is endothermic. Removing H_₂ from ethane to give ethylene needs energy, so (c) is endothermic. Diamond lies above graphite in energy (Δ_f H^° of diamond ≈ +1.9 kJ/mol), so the conversion of graphite to diamond is endothermic, (d).

Therefore, the endothermic processes are (b), (c), and (d).