Question

For a glass marginally below its glass transition temperature, which one of the following statements is true?

• A. Glass has higher enthalpy than both the corresponding crystalline and liquid phases
• B. Glass has lower enthalpy than both the corresponding crystalline and liquid phases
• C. Glass has higher entropy than the corresponding crystalline phase and lower entropy than the corresponding liquid phase
• D. Glass has lower entropy than the corresponding crystalline phase and higher entropy than the corresponding liquid phase

Hint:

Near the glass transition temperature, remember the order of entropy: crystal<glass<liquid. This helps eliminate options quickly.

Answer 1

The Correct Option is C

At temperatures just below the glass transition temperature \(T_g\), the glass behaves like a frozen supercooled liquid.
Its structure is disordered like a liquid but with the atomic mobility drastically reduced.
Entropy ranking for phases of the same material follows:
\[ S_{\text{crystal}}<S_{\text{glass}}<S_{\text{liquid}} \]
A crystalline solid has an ordered lattice and hence the lowest entropy.
A liquid has maximum disorder and thus the highest entropy.
A glass is intermediate—it retains some structural disorder relative to a crystalline solid, but is less disordered than the liquid state.
Therefore, glass has higher entropy than the crystalline phase and lower entropy than the liquid phase.
Hence, option (C) is correct.