Question

Consider a pure crystalline solid that is heated from absolute zero to a temperature above the boiling point of the liquid.

Which of the following processes produces the greatest increase in the entropy of the substance?

a. melting the solid

b. heating the liquid

c. heating the gas

d. heating the solid

e. vaporizing the liquid

Answer 1

Entropy of a substance is a measure of randomness. When we heat a solid, the randomness increase very little because the position of particles in lattice is still more or less fixed. There is only some scope of vibration.

When it is melted to liquid, the entropy increase considerably because of phase change. But still, the entropy increase is limited because particles still experience a good amount of intermolecular force.

Similarly, heating the liquid, does increases randomness but not as much as compared to phase change which happens when liquid is vaporized. Vapours have greatest level of disorder and have very little intermolecular force. Thus, entropy change in the case of vaporisation is the maximum.

So, the answer will be (e) Vaporizing the liquid