Ways in which a chemical reaction can be informative:

(i) Indicating the physical state of reactants and products. Example: (g) denotes the gaseous state.

Zn (s) + H₂SO₄ (aq.) → ZnSO₄ (aq.) + H₂ (g)

(ii) Indicating Heat change. For example: writing "+Heat" or "+Heat energy" or "+Energy" on the products side of an equation denotes exothermic reaction.

C(s) + O₂ (g) → CO₂ (g) + Heat

(iii) Indication of the "conditions" under/in which the reaction takes place.

Example: Heat is denoted by delta which is written over the arrow in an equation.