Question

Define a chemical reaction. State four observations which help us to determine that a chemical equation has taken place. Write one example of each observation with a balanced chemical equation.​

Answer 1

Answer :

• Chemical reaction : A process in which two or more substances react to form some other new substances with a new set of properties is called a chemical reaction.

$\hrulefill$

Four observation which help us to determine that a chemical reaction has taken place are:-

(1) Evolution of a gas: The reaction between zinc and dil. sulphuric acid -

• $\rm{Zn_{(s)}+H_2SO_{4(aq)}\longrightarrow{}ZnSO_{4(aq)}+H_{2(g)}}$

(2) Change in colour: The chemical reaction between potassium iodide solution and lead nitrate solution -

• $\rm{Pb(NO_3)_{2(aq)}+2KI\longrightarrow{}2KNO_{3(aq)}+PbI_{2(s)}}$

(3) Formation of precipitate: The chemical reaction between sulphuric acid and barium chloride solution -

• $\rm{BaCl_{2(aq)}+H_2SO_{4(aq)}\longrightarrow{}2HCl_{(aq)}+BaSO_{4(s)}}$

(4) Change in temperature: The chemical reaction between quick lime and water -

• $\rm{CaO_{(s)}+H_2O_{(l)}\longrightarrow{}Ca(OH)_{2(aq)}+Heat}$