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Ch.19 - Chemical Thermodynamics
All textbooksBrown 14th EditionCh.19 - Chemical ThermodynamicsProblem 106
Chapter 19, Problem 106

The following processes were all discussed in Chapter 18, “Chemistry of the Environment.” Estimate whether the entropy of the system increases or decreases during each process: (a) photodissociation of O₂(g). (b) formation of ozone from oxygen molecules and oxygen atoms. (c) diffusion of CFCs into the stratosphere. (d) desalination of water by reverse osmosis.

Verified step by step guidance
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Step 1: Understand the concept of entropy. Entropy is a measure of the disorder or randomness in a system. Generally, processes that increase disorder increase entropy, while those that decrease disorder decrease entropy.
Step 2: Analyze process (a) - photodissociation of O₂(g). Photodissociation involves breaking a molecule into smaller parts. Since breaking O₂ into individual oxygen atoms increases the number of particles and disorder, the entropy of the system increases.
Step 3: Analyze process (b) - formation of ozone from oxygen molecules and oxygen atoms. This process involves combining O₂ molecules with O atoms to form O₃. Since this reduces the number of gas particles, the entropy of the system decreases.
Step 4: Analyze process (c) - diffusion of CFCs into the stratosphere. Diffusion is the spreading of particles from an area of high concentration to low concentration, increasing disorder. Therefore, the entropy of the system increases.
Step 5: Analyze process (d) - desalination of water by reverse osmosis. Reverse osmosis involves removing salt from water, which decreases the disorder of the system by separating mixed components, thus decreasing the 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. In thermodynamics, it quantifies the number of possible arrangements of particles in a system, with higher entropy indicating greater disorder. Understanding how entropy changes during chemical processes helps predict the spontaneity and direction of reactions.
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Photodissociation

Photodissociation is the process by which a chemical compound is broken down into its components by the absorption of light. In the case of O₂(g), this process involves the breaking of the O=O bond, leading to an increase in the number of gas particles, which typically results in an increase in entropy due to greater molecular freedom.

Diffusion

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration, driven by the concentration gradient. This process increases the entropy of a system as particles spread out and occupy a larger volume, leading to a more disordered state. In the context of CFCs diffusing into the stratosphere, this results in an increase in entropy.
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Related Practice
Textbook Question
In chemical kinetics, the entropy of activation is the entropy change for the process in which the reactants reach the activated complex. Predict whether the entropy of activation for a bimolecular process is usually positive or negative.
Textbook Question

At what temperatures is the following reaction, the reduction of magnetite by graphite to elemental iron, spontaneous? Fe3O4(s) + 2 C(s, graphite) → 2 CO2(g) + 3 Fe(s)

Textbook Question

An ice cube with a mass of 20 g at -20 °C (typical freezer temperature) is dropped into a cup that holds 500 mL of hot water, initially at 83 °C. What is the final temperature in the cup? The density of liquid water is 1.00 g>mL; the specific heat capacity of ice is 2.03 J>g@C; the specific heat capacity of liquid water is 4.184 J>g@C; the enthalpy of fusion of water is 6.01 kJ>mol.

Textbook Question
Carbon disulfide 1CS22 is a toxic, highly flammable substance. The following thermodynamic data are available for CS21l2 and CS21g2 at 298 K: (e) Use the data in the table to calculate ΔS° at 298 K for the vaporization of CS21l2. Is the sign of ΔS° as you would expect for a vaporization?
Textbook Question
The following data compare the standard enthalpies and free energies of formation of some crystalline ionic substances and aqueous solutions of the substances:
(a) Write the formation reaction for AgNO31s2. Based on this reaction, do you expect the entropy of the system to increase or decrease upon the formation of AgNO31s2? (b) Use ΔH°f and ΔG°f of AgNO31s2 to determine the entropy change upon formation of the substance. Is your answer consistent with your reasoning in part (a)?