1. X is Copper (Cu). The black compound is Copper Oxide
(CuO).
$2Cu(s) + O_2(g) \xrightarrow{\Delta} 2CuO(s)$
2. X is Calcium Oxide (CaO) or Quick Lime. Used in cement.
$CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq) + Heat$
Ca(OH)$_2$ is Calcium Hydroxide (basic).
3. X is Zinc (Zn).
Y is Hydrogen gas
(H$_2$).
$Zn(s) + H_2SO_4(aq) \rightarrow ZnSO_4(aq) + H_2(g)$
4. X is Silver (Ag). The reaction is Photolytic
Decomposition.
$2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g)$
5. A is Sodium Bicarbonate (Baking Soda, $NaHCO_3$). On
heating it gives $Na_2CO_3$, $H_2O$ and $CO_2$.
6. Salt is Ferrous Sulphate ($FeSO_4 \cdot 7H_2O$). Green crystals.
$2FeSO_4(s) \xrightarrow{\Delta} Fe_2O_3(s) + SO_2(g) + SO_3(g)$
Reddish brown residue is Ferric Oxide ($Fe_2O_3$).
7. (a) 'X' is Calcium Oxide ($CaO$, Quick lime). (b)
$CaO + H_2O \rightarrow Ca(OH)_2$
8.
$3Fe + 4H_2O \rightarrow Fe_3O_4 + 4H_2$
(Balancing)
9.
$3MnO_2 + 4Al \rightarrow 3Mn + 2Al_2O_3 + Heat$
(Thermite/Displacement)
10.
$2Pb(NO_3)_2 \xrightarrow{\Delta} 2PbO + 4NO_2 + O_2$
(Thermal Decomposition)
11.
$CO(g) + 2H_2(g) \xrightarrow{340 atm} CH_3OH(l)$
12.
$Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)$
(Precipitation)
13. Iron is more reactive than copper; it displaces Cu from CuSO$_4$.
$Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$
14. During respiration, glucose breaks down in the presence of oxygen to
release energy (ATP). Since heat/energy is released, it is exothermic.
15. To prevent oxidation (rancidity) which causes bad smell and taste.
Nitrogen is an inert gas.
16. Combination involves reactants joining to form one product. Decomposition
involves one reactant breaking into multiple products. Hence they are opposite.
17. $Fe_2O_3 \cdot xH_2O$.
18. Presence of Oxygen (Air) and Moisture (Water).
19. Painting and Galvanisation.
20. Oxidation. (Iron gains oxygen).
21. Thermite Reaction (Displacement). It is highly exothermic, producing
molten iron which fills gaps in tracks.
