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