Question

Imran and Rohan are best friends. They study in different schools in Srianagar in Kashmir. Imran has just entered class IX whereas Rohan is a student of class X. This year, winter is very severe in Kashmir, So, imran Rohan were discussing the central heating systens, which could be used to heat their homes during severe cold in this winter season. Imran said that they can use boiling hot water in hot water radiators for the central heating of their homes in water. Rohan, however, did not agree with Imran. Rohan said that he, however, does not know the practical implications of his recommendation.
(a) What is the temperature of boiling water under normal conditions ?
(b) What is the temperature of steam formed from boiling water under normal conditions ?
(c) Out of boiling water and steam, which causes more severe burns on the skin and why ?
(d) State whether boiling water or steam is better for central heating in homes during extreme water. Give your choice.
(f) What values are displayed by Rohan in this episode ?

Answer 1

(a) The temperature of boiling water under normal conditions is `100^(@)C`
(b) The temperature of steam (formed from boiling water) under normal conditions is also `100^(@)C`
(c) Steam (at `100^(@)C`) causes more severe burns than boiling water (at the same temperature of `100^(@)C`) because steam contains more heat in the form of latent heat of vaporisation (than boiling water). So, when steam falls on our skin and condenses to form water, it gives `22.5 xx 10^(5)` joules per kilogram more heat than boiling water at the same temperature. Since steam gives out more heat than boiling water, therefore, it causes more severe burns
(d) Theoretically, steam is better for central heating purposes than boiling water. This is because steam contains more heat (in the form of latent heat) than boiling water.
(e) A change of state will take place in the case of steam. When steam gets cooled, it changes into water. So, a change in state from gas (or vapour) to liquid takes places. The special name of this change of state from steam to water is condensation.
(f) Ther various values displayed by Rohan in this eposode are (i) Knowledge of latent heat of steam (ii) Application of knowledge to solve everday problems, and (iii) Desire to protect his family from severe cold in winter.