Question

Which of the following conditions regarding the chemical process ensures its spontaneity at all temperatures?

• A. \(\Delta H<0; \Delta S<0\)
• B. \(\Delta H>0; \Delta S<0\)
• C. \(\Delta H<0; \Delta S>0\)
• D. \(\Delta H>0; \Delta S>0\)

Hint:

Think of it as: exothermic (\(\Delta H<0\)) and increasing disorder (\(\Delta S>0\)) will always favor a spontaneous process.

Answer 1

The Correct Option is C

Step 1: Basic Principle
Spontaneity of a process is determined by Gibbs free energy change: \(\Delta G = \Delta H - T\Delta S\). For spontaneity, \(\Delta G<0\).
Step 2: Solution Procedure:

(A) \(\Delta H<0, \Delta S<0\): \(\Delta G\) is negative at low temperatures, positive at high temperatures. Spontaneous only at low temperatures.
(B) \(\Delta H>0, \Delta S<0\): \(\Delta G\) is always positive. Non-spontaneous at all temperatures.
(C) \(\Delta H<0, \Delta S>0\): \(\Delta G\) is always negative. Spontaneous at all temperatures.
(D) \(\Delta H>0, \Delta S>0\): \(\Delta G\) is negative at high temperatures, positive at low temperatures. Spontaneous only at high temperatures.

Step 3: Required Answer:
The condition for spontaneity at all temperatures is \(\Delta H<0\) and \(\Delta S>0\), option (C).