Which of the reactions are exothermic? agcl(s)⟶ag+(aq)+cl−(aq) δh=127 kj/mol nh3(g)+hcl(g)⟶nh4cl(s) δh=−176 kj/mol 2fe2o3(s)+3c(s)⟶4fe(s)+3co2(g) δh=468 kj/mol 2mg(s)+o2(g)⟶2mgo(s) δh=−1203 kj/mol c(graphite)+o2(g)⟶co2(g) δh=−393.5 kj/mol ch4(g)+2o2(g)⟶co2(g)+2h2o(l)δh=−891 kj/mol?

Exothermic reactions are chemical reactions that proceed with the release of heat energy. I contrast, endothermic reactions involve absorption of heat.

The enthalpy change (ΔH) for exothermic reactions is negative while that of endothermic reactions is positive.

In the given examples, reactions that show a negative ΔH are:

NH3 + HCl NH4Cl  ΔH = -176 KJ/mol

2Mg + O2 2MgO  ΔH = -1203 kj/mol

C + O2 CO2 ΔH = -393.5 kj/mol

CH4 + 2O2 CO2 + 2H2O  ΔH = -891 kj/mol