Question

Ex.Q.3 Explain the following terms with examples.
a.Endothermic reaction
b.Displacement reaction

Answer 1

a. Endothermic reaction: In endothermic reaction, heat is either absorbed from the surroundings or heat has to supplied from outside. It means an endothermic reaction needs or takes in heat to continue.
For example: When a solid ammonium chloride ($N{H}_{4}Cl$) is dissolved into water, you will observe that the tube becomes colder.
$N{H}_{4}Cl\left(s\right)+H_{2}O\to N{H}_{4}Cl\left(aq\right)–Heat$
In the above reaction, heat is absorbed from surroundings.

b.Displacement reaction: The reaction in which the ion of a more reactive element displaces the ion of a less reactive metal by forming its own ions. Such reaction is called displacement reaction.
In short, displacement reaction is a reaction in which a more reactive element displaces the less reactive element to form its new compound.

$CuS{O}_4+Zn\to ZnS{O}_4+Cu$
In the reaction, $Z{n}^{2+}$ ions formed from Zn atoms take the place of $C{u}^{2+}$ ions in copper sulphate (zinc is more reactive).
It means that Zn displaces Cu from $CuS{O}_4.$