Question

State four observations that help to determine whether a chemical reaction has taken place
or not. Write one example of each observation with a balanced chemical equation.

Answer 1

Answer:

Process in which new substances with new properties are formed by the rearrangement of atoms is known as a chemical reaction.

(i) Evolution of gas: The chemical reaction between zinc and dilute H2SO4. Zn(s)+H2SO4(aq) → ZnSO4(sq) +H2(g)↑

(ii) Change in colour: The chemical reaction between potassium iodide solution and lead nitrate solution. Pb(NO3)2(aq)+2KI → 2KNO3(aq)+PbI2(s) Pb(NO3)2(aq)+2KI - Colourless PbI2(s)-Yellow

(iii) Formation of piecipitate : The chemical reaction between sulphuric acid barium chloride solution. BaCl2(aq) + H2SO4(aq) → 2HCl(aq) + BaSO4(s) 2HCl(aq) + BaSO4(s)- White precipitate

(iv) Change in temperature : The ctremiial reaction between quick lime and water. CaO(s)+H2O(l) → Ca(OH)2(aq)+Heat CaO(s)

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