Multiple Choice
Which of the following conditions must be met for the entropy of a pure solid to be zero according to the Third Law of Thermodynamics?
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19. Chemical Thermodynamics
Third Law of Thermodynamics
Multiple Choice
How does the third law of thermodynamics allow absolute entropies of substances to be determined?
A
It states that the entropy of a system increases in all spontaneous processes.
B
It states that the entropy of a perfect crystal at 0 K is zero, providing a reference point for measuring absolute entropy.
C
It relates the change in entropy to the heat absorbed at constant pressure.
D
It allows entropy to be calculated from the enthalpy and temperature of a substance.
Verified step by step guidance1
Understand that the third law of thermodynamics provides a fundamental reference point for entropy measurements by stating that the entropy of a perfect crystal at absolute zero temperature (0 K) is exactly zero.
Recognize that this zero-entropy reference allows scientists to assign absolute entropy values to substances by measuring how entropy changes as temperature increases from 0 K to the temperature of interest.
Use calorimetric data and heat capacity measurements to calculate the entropy change from 0 K to the desired temperature by integrating the heat capacity over temperature, according to the formula: \(S = \int_0^T \frac{C_p}{T} \, dT\).
Combine the zero entropy at 0 K with the integrated entropy changes to determine the absolute entropy of a substance at any temperature above 0 K.
Note that this approach contrasts with relative entropy changes, which only measure differences between states, whereas the third law enables determination of absolute entropy values.
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