How to Justify the Second Law of Thermodynamics – Part 2

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, ΔGѲ < 0. The phrase ‘thermodynamically favored’ is preferred instead so that common misunderstandings equating ’spontaneous’ with ‘suddenly’ or ‘without cause’ can be avoided.

Question:

For oxidation of iron,

4Fe(s) + 3O2(g) → 2Fe2O3(s)

entropy change is – 549.4 J K–1 mol–1 at 298 K. In spite of negative entropy change of this reaction, can the reaction be explained for spontaneity in terms of entropy (DrHѲ = –1648 × 103 J mol–1)?

Solution:



Click/tap to enlarge the image

ΔStot = Total change in entropy of the universe, T = Absolute temperature, ΔSsurr = Change in entropy of the surroundings, ΔSsys = Change in entropy of the system

Justified the 2nd law❓ Let Chemaficionado know in the comments below or at mychemistryhomework@gmail.com❗

Reference:

(1)    Wikipedia Contributors. Entropy. Wikipedia. https://en.wikipedia.org/wiki/Entropy.

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

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