Q111 / 240 · KCET 2026 · Chemistry

A: Entropy of a perfect crystalline solid at absolute zero approaches zero.
B: For spontaneity of a reaction, $T\Delta S > \Delta H$.
Among the two statements given above, identify the correct answer from the options given below.

  • Correct answer
    A
    Both '$A$' and '$B$' are true
  • B
    'A' is true but 'B' is false
  • C
    Both 'A' and 'B' are false
  • D
    '$A$' is false but '$B$' is true

Solution

Statement A is based on the third law of thermodynamics, which states that the entropy of a perfectly crystalline solid approaches zero as the temperature approaches absolute zero. Thus, Statement A is true.

For a reaction to be spontaneous at constant temperature and pressure, the change in Gibbs free energy ($\Delta G$) must be negative ($\Delta G < 0$).

From the Gibbs-Helmholtz equation:
$\Delta G = \Delta H - T\Delta S$

For spontaneity, $\Delta G < 0$
$\Rightarrow \Delta H - T\Delta S < 0$
$\Rightarrow T\Delta S > \Delta H$

Thus, Statement B is also true.

Both Statement A and Statement B are true.

Answer: Both '$A$' and '$B$' are true

Hence, the correct answer is option: 'A'.

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