Question

give an example of each of the following chemical changes.
(a) A reaction involving
(i) change of state
(ii) formation of precipitate
(b) An exothermic and an endothermic reaction involving carbon as one of the reactants.
(c) A reaction where colour change is noticed.​

Answer 1

Answer:

In simple terms, the endothermic reactions absorb energy from the surrounding that is in the form of heat. On the other hand, an exothermic reaction releases energy into the surrounding of the system. A popular example of an endothermic chemical reaction is photosynthesis.

Answer 2

Answer:

(a) (i) C(s)+ 2S → CS2(l)

(ii) FeSO4 (aq) + 2NaOH (aq) → Fe(OH)2↓+Na2SO4 (aq)

(b) Exothermic reaction: When carbon burns in oxygen to form carbon dioxide, a lot of heat is produced.

C + O2 → CO2 + Heat

Endothermic reaction: When carbon is heated with sulphur at high temperature, liquid carbon disulphide is formed.

C + 2S + heat → CS2

(c) Cu (s) (brown) + 2H2SO4 (aq) → CuSO4 (aq) (blue)+ 2H2O (l) +SO2