Three observations which determine that a chemical reaction has taken place are :
(i) Change in state and colour.
(ii) Evolution of gas.
(iii) Change in temperature.
Three informations that cannot be obtained about a chemical reaction, merely by its chemical equation
(i) The state of a matter of the reactants and products.
(ii) Amount of heat evolved or absorbed in a reaction
(iii) The change of colour after the chemical reaction.