Chemical equations can be made more informative by expressing the following characteristics of the reactants and products.
1) Physical state
ii) Heat exchange (exothermic or endothermic change)
iii) Gas evolved (if any)
iv) Precipitate formed (if any)
i) Expressing the physical state : The physical state of the substances may be mentioned along with their chemical formulae. The different states i.e., gaseous, liquid and solid states are represented by the notations (g), (Z) and (s) respectively. If the substance is present as a solution in water, it is represented as (aq).
ii) Heat exchange : Heat is liberated in exothermic reactions arid heat is absorbed in endothermic reactions.
iii) Gas evolved : If a gas is evolved in a reaction, it is denoted by an upward
arrow or (g).
iv) Precipitate formed : If a precipitate is formed in the reaction, it is denoted by a downward arrow