Give an example of each of the following chemical changes.
(a) A reaction involving.
(i) Change of state.
(ii) Formation of the precipitate.
(b) An exothermic and an endothermic reaction involving carbon as one of the reactants.
(c) A reaction where the colour change is noticed.
Give an example of each of the following chemical changes.
(a) A reaction involving.
(i) Change of state.
(ii) Formation of the precipitate.
(b) An exothermic and an endothermic reaction involving carbon as one of the reactants.
(c) A reaction where the colour change is noticed.
(a)
(i) Change of state: Combustion of candle wax is characterized by a change in state from solid to liquid and gas.
(ii) Formation of precipitate: Reaction between potassium iodide and lead nitrate forms a yellow precipitate of lead iodide.
Change in temperature: Reaction between zinc granules and dilute hydrochloric acid.
Ca(OH)2(aq) +CO2 → CaCO3(s) 【precipitate】+H2O(I)
(b) Exothermic reaction: Reactions which proceeds with the release of energy are called exothermic reactions.
C + O2 → CO2 + Energy
Endothermic reaction: Reactions which proceeds with the absorption of energy are called endothermic reactions.
C + 2S + Energy → CS2
(c) A chemical change may not always be visible to the human eye but at times, it so happens that the colour of chemicals changes after undergoing a chemical change. When two or more substances combine to react, they produce a different structure, which has the totally different composition and colour.
Example:
The reaction of iron and copper sulphate
CuSO4 + Fe → FeSO4 + Cu
(Blue) (Green)
Colour changes from blue to light green.
(a)
(i) Change of state: Combustion of candle wax is characterized by a change in state from solid to liquid and gas.
(ii) Formation of precipitate: Reaction between potassium iodide and lead nitrate forms a yellow precipitate of lead iodide.
Change in temperature: Reaction between zinc granules and dilute hydrochloric acid.
Ca(OH)2(aq) +CO2 → CaCO3(s) 【precipitate】+H2O(I)
(b) Exothermic reaction: Reactions which proceeds with the release of energy are called exothermic reactions.
C + O2 → CO2 + Energy
Endothermic reaction: Reactions which proceeds with the absorption of energy are called endothermic reactions.
C + 2S + Energy → CS2
(c) A chemical change may not always be visible to the human eye but at times, it so happens that the colour of chemicals changes after undergoing a chemical change. When two or more substances combine to react, they produce a different structure, which has the totally different composition and colour.
Example:
The reaction of iron and copper sulphate
CuSO4 + Fe → FeSO4 + Cu
(Blue) (Green)
Colour changes from blue to light green.
