Which reaction is exothermic? CH4 + 2O2 Right arrow. CO2 + 2H2O + 891 kJ NH4NO3 + H2O + 25 kJ Right arrow. NH4+(aq) + NO3-(aq) 2H2O + 286 kJ Right arrow. 2H2 + O2 N2 + O2 + 181 kJ Right arrow. 2NO