Question

For which of the following pure chemical substances will S° be exactly equal to 0.0 J/molK at T = 0. K? Explain

            a) CaO(s)

            b) Fe(s)

            c) I₂(s)

            d) both b and c

            e) both a and b and c

Answer 1

We know that, the entropy of a pure, perfect crystal at absolute zero temperature ( 0 Kelvin) is always zero because they have only 1 minimum energy state or microstate.

This happens because, as the third law of thermodynamics says that the entropy decreases as the temperature approaches absolute zero values. And at exact absolute zero that is 0 Kelvin, entropy if perfect and pure crystals are 0. So, since CaO is perfect crystalline solid and I2 and Fe are pure elements they will have 0 entropy.

Hence the answer is:

(e) both a and b and c

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