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Ch.19 - Chemical Thermodynamics
All textbooksBrown 14th EditionCh.19 - Chemical ThermodynamicsProblem 35
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Chapter 19, Problem 35

Does the entropy of the system increase, decrease, or stay the same when (a) a solid melts, (b) a gas liquefies, or (c) a solid sublimes?

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1
Step 1: Understand the concept of entropy. Entropy is a measure of the disorder or randomness in a system. In general, the more disordered a system, the higher its entropy.
Step 2: Analyze the process of a solid melting. When a solid melts, it transitions from a highly ordered state (solid) to a less ordered state (liquid). This increase in disorder means the entropy of the system increases.
Step 3: Examine the process of a gas liquefying. When a gas condenses into a liquid, it goes from a less ordered state (gas) to a more ordered state (liquid). This decrease in disorder means the entropy of the system decreases.
Step 4: Consider the process of a solid subliming. Sublimation is the transition from a solid directly to a gas. This process involves moving from a highly ordered state (solid) to a very disordered state (gas), resulting in an increase in entropy.
Step 5: Summarize the changes in entropy for each process: (a) Melting increases entropy, (b) Liquefying decreases entropy, and (c) Subliming increases entropy.
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Related Practice
Open Question
(a) Using the heat of vaporization in Appendix B, calculate the entropy change for the vaporization of water at 25 °C and at 100 °C. (b) From your knowledge of microstates and the structure of liquid water, explain the difference in these two values.
Open Question
(a) What do you expect for the sign of ΔS in a chemical reaction in which 2 mol of gaseous reactants are converted to 3 mol of gaseous products? (b) For which of the processes in Exercise 19.11 does the entropy of the system increase?
Textbook Question

(a) In a chemical reaction, two gases combine to form a solid. What do you expect for the sign of ΔS?

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Open Question
Does the entropy of the system increase, decrease, or stay the same when (a) the temperature of the system increases, (b) the volume of a gas increases, and (c) equal volumes of ethanol and water are mixed to form a solution?
Open Question
Indicate whether each statement is true or false. (a) The third law of thermodynamics says that the entropy of a perfect, pure crystal at absolute zero increases with the mass of the crystal. (b) “Translational motion” of molecules refers to their change in spatial location as a function of time. (c) “Rotational” and “vibrational” motions contribute to the entropy in atomic gases like He and Xe. (d) The larger the number of atoms in a molecule, the more degrees of freedom of rotational and vibrational motion it likely has.
Textbook Question

Indicate whether each statement is true or false. (a) Unlike enthalpy, where we can only ever know changes in H, we can know absolute values of S. (b) If you heat a gas such as CO2, you will increase its degrees of translational, rotational and vibrational motions. (c) CO2(g) and Ar(g) have nearly the same molar mass. At a given temperature, they will have the same number of microstates.

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