Write the chemical equation of the reaction with an example each in which the following change has taken place:
(i) Change in colour
(ii) Change in temperature
(iii) Formation of precipitate.

Explanation

(i) Change in colour : Reaction between lead nitrate solution and potassium iodide solution.
`Pb(NO_(3))_(2)(aq)+2KIrarrPbI_(2)(S)+2KNO_(3)(aq)`
In this reaction, colour changes from colourles to yellow.
(ii) Change in temperature : Action of dilute sulphuric acid on zinc.
`Zn(S)+H_(2)SO_(4)(aq)rarrZnSO_(4)(aq)+H_(2)`
In this reaction, heat is evolved
(iii) Formation of precipitate : Action of barium chloride on sodium sulphate .
`BaCl_(2)(aq)+Na_(2)SO_(4)(aq)rarrBaSO_(4)(S)+2NaCl(aq)(ppt.)`