Question

Explain the factors affecting

(a) melting point

(b) boiling point

(c) evaporation

Answer 1

Step-I

(i) Melting point $\Rightarrow$It can be explained as that temperature at which the solid changes into liquid at the atmospheric pressure. For Example $\Rightarrow$ ice melts at $0^{\mathrm{o}}\mathrm{C}$ to form water.

(ii) Factor affecting melting point:-

(a) Effect of pressure $\Rightarrow$It depends upon the nature of the solid.

(1) If the solids are expanding on melting then by increasing the pressure, an increase in melting point is also seen. This is because the increase in pressure is opposing the expansion.

Example $\Rightarrow$Silver $\left(\mathrm{Ag}\right)$, Gold$\left(\mathrm{Au}\right)$, Copper$\left(\mathrm{Cu}\right)$ etc.

(2) If the solids are contracting on melting then by increasing the pressure, a decrease in melting point will be seen. This is because the increase in pressure is favoring the contraction.

Example$\Rightarrow$Ice, Brass(mixture of Copper & Zinc).

(b) Effect of addition of impurities$\Rightarrow$ By adding impurities to a solid then the melting point of the solid decreases. It means that the substance can melt at a lower temperature.

For Example $\Rightarrow$ Rose's metal is an alloy of tin $\left(\mathrm{Sn}\right)$ , lead $\left(\mathrm{Pb}\right)$ and bismuth $\left(\mathrm{Bi}\right)$.

Step-II

(i) Boiling point$\Rightarrow$ Boiling point is that point at which the liquid boils and changes into gaseous state at the atmospheric pressure.

(ii) Factors affecting boiling point:-

(a) Effect of pressure$\Rightarrow$ When we increase the external pressure then the boiling point of the liquid will also increase.

For Eg. $\Rightarrow$ Water boils at a lower temperature than${100}^{\mathrm{o}}\mathrm{C}$ at higher altitudes.

(b) Effect of impurities$\Rightarrow$ When we add solid substances in a liquid then the boiling point of the liquid increases beyond the normal boiling point.

For Example $\Rightarrow$ When the common salt is dissolved in water, then the solution boils at a temperature greater than ${100}^{\mathrm{o}}\mathrm{C}$.

Step-III

(i) Evaporation $\Rightarrow$ Evaporation can be defined as the process when the liquid is changing into vapors even below its boiling point.

For Example $\Rightarrow$ Drying clothes in the sun.

(ii) Factors affecting Evaporation:-

(a) Surface area $\Rightarrow$ By increase in surface area, the rate of evaporation will be increased.

(b) Temperature $\Rightarrow$ By increase in the temperature, the rate of evaporation will be increased.

(c) Humidity $\Rightarrow$ Humidity can be considered as the amount of water vapors that the atmospheric air holds. So, higher humidity will decrease the rate of evaporation.

(d) Wind Speed $\Rightarrow$ The increment in wind speed will increase the rate of evaporation.