Question

(a)What is a balanced chemical equation? Why should chemical equations be balanced?

(b)Write the chemical equation of the reaction in which the following changes have taken place.

(i) Change in color. (ii) Change in temperature.​

Answer 1

(a)

A chemical equation needs to be balanced because a chemical reaction is just a rearrangement of atoms. Atoms themselves are neither created nor destroyed during the course of a chemical reaction. The chemical equation needs to be balanced to follow the law of conservation of mass.

(b)

(i) Change in colour:

Reaction between lead nitrate solution and potassium iodide solution.

Pb(NO3)2(aq)+2KI → PbI2(s)+2KNO3(aq)

In this reaction, colour changes from colourless to yellow. (ii)Change in temperature: Action of dilute sulphuric acid on zinc.

Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2

In this reaction, heat is evolved

(iii) Formation of precipitate:

Action of barium chloride on sodium sulphate.

BaCl2(aq) +Na2SO4(aq) → BaSO4(s) +2NaCl(aq) BaSO4(s) - ppt

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