How to Justify the Second Law of Thermodynamics – Part 3

The second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system.

In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems NEVER decreases.

The term ‘spontaneous’ has historically been used to describe processes for which the change in Gibbs free energy in the standard state, ΔG^Ѳ < 0. The phrase ‘thermodynamically favored’ is preferred instead so that common misunderstandings equating ’spontaneous’ with ‘suddenly’ or ‘without cause’ can be avoided.

Question:

As a sample of KNO₃(s) is stirred into water at 25°C, the compound dissolves endothermically. How would you explain why the process is thermodynamically favorable at 25°C?

Solution:

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ΔH^Ѳ = Standard change in enthalpy, T = Absolute temperature, ΔS^Ѳ = Standard change in entropy

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References:

(1)    Wikipedia Contributors. Laws of thermodynamics. Wikipedia. https://en.wikipedia.org/wiki/Laws_of_thermodynamics.

(2)    Ncert. Chemistry : Textbook for Class XI - Part.I; National Council Of Educational Research And Training: New Delhi.