If the balanced equation is to look complete in all respects, then we have to put all the states of the species, the conditions of reactions. (s) : solid(insoluble solid) (l) : liquid (g) : gas (aq.): aqueous (soluble in water) $$CaCO_3(s) + heat \xrightarrow{1070-1270K} CaO(s) + CO_2(g)$$ $$N_2(g) + 3H_2(g) \xrightarrow[700K/200 atm]{FeO(k_2O + Al2O_3)} 2NH_3(g) + 22.4 Kcals$$ $$NaOH(aq.) + HCl(aq) \rightarrow NaCl(aq.) + H_2O(l) + 13.6 kcals$$ In the first example, heat is absorbed (endothermic reaction) and the in the 2^nd^ and 3^rd^ examples, heat is liberated (exothermic reactions). **IMPORTANCE OF A BALANCED CHEMICAL EQUATION:** Besides giving the reactants and products, a balanced equation gives the following. (a) Reaction Stoichiometry: How many atoms or molecules of the reactants undergo chemical reactions to produce how many atoms or molecules of the products. $$2KClO_3 \rightarrow 2KCl + 3O_2$$ From the above example, we understand that 2 molecules (actually 2