According to the Third Law of Thermodynamics, what is the entropy of a pure, perfectly crystalline substance at absolute zero of temperature (0 Kelvin)?
Answer and explanation
Correct answer: B. Zero (S = 0)
- Step 1: Max Planck formulated the Third Law of Thermodynamics based on statistical mechanics and Nernst's heat theorem.
- Step 2: At absolute zero (), all thermal molecular vibrations and rotations cease.
- Step 3: In a perfectly crystalline substance with zero defects or isotopic mixing, there is only one microstate available to the system ().
- Step 4: According to Boltzmann's entropy formula, .
- Step 5: This provides an absolute reference baseline () allowing the determination of absolute standard entropies of chemical substances.
Answer
Zero (S = 0)
Why not the others: 'Approaching infinity' is the opposite of perfect order; 'A constant value equal to 1.0' contradicts the fundamental definition of the zero-entropy state; 'Negative infinity' is impossible since statistical microstate counts make .
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