Question
What is a thermochemical equation? Give two examples.
Solution
Most chemical reactions are accompanied by either evolution or absorption of heat. These reactions are known as exothermic and endothermic reactions respectively.
Such an equation in which information about heat change is included is called a thermochemical equation. It is very important in such a case to indicate the physical state of the various species involved.
Examples are:
(i) C(s) + O2(g) →CO2(g) ; ΔH = -393.5 kJ
(Exothermic reaction) In this heat evolved during the reaction
(ii) C(graphite) + 2H2(g) →CH4(g); ΔH = + 74.25 kJ
(Endothermic reaction):In this heat is supplied to the reaction
