Textbook Question
(a) In a chemical reaction, two gases combine to form a solid. What do you expect for the sign of ΔS?
Ch.19 - Chemical Thermodynamics
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?
Verified step by step guidance1
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.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Entropy
Entropy is a measure of the disorder or randomness in a system. It quantifies the number of possible arrangements of particles in a system, with higher entropy indicating greater disorder. In thermodynamics, processes that increase the number of accessible microstates typically lead to an increase in entropy.
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Entropy in Thermodynamics
Phase Changes
Phase changes refer to the transitions between solid, liquid, and gas states of matter. Each phase has distinct properties and energy levels. During these transitions, such as melting or sublimation, the arrangement and energy of particles change, which directly affects the entropy of the system.
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Second Law of Thermodynamics
The Second Law of Thermodynamics states that in any energy transfer or transformation, the total entropy of an isolated system can never decrease over time. This principle implies that natural processes tend to move towards a state of greater disorder, influencing how we understand the changes in entropy during phase transitions.
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Related Practice
Textbook Question
(b) How does the entropy of the system change in the processes described in Exercise 19.12?
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.