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Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium
McMurry - Chemistry 8th Edition
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Tutti i libri di testoMcMurry 8th EditionCh.18 - Thermodynamics: Entropy, Free Energy & EquilibriumProblema 143m
Capitolo 18, Problema 143m

Methanol (CH3OH) is made industrially in two steps from CO and H2. It is so cheap to make that it is being considered for use as a precursor to hydrocarbon fuels, such as methane (CH4):
Step 1. CO(g) + 2 H2(g) S CH3OH(l) ΔS° = - 332 J/K
Step 2. CH3OH1l2 → CH4(g) + 1/2 O2(g) ΔS° = 162 J/K
(m) If you were designing a production facility, would you plan on carrying out the reactions in separate steps or together? Explain.

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The problem involves two reactions: the formation of methanol from carbon monoxide and hydrogen, and the conversion of methanol to methane and oxygen. Each reaction has an associated change in entropy (ΔS°).
For Step 1, the reaction has a negative entropy change (ΔS° = -332 J/K), indicating a decrease in disorder. For Step 2, the reaction has a positive entropy change (ΔS° = 162 J/K), indicating an increase in disorder.
A negative ΔS° suggests that the reaction may be more favorable at lower temperatures, while a positive ΔS° suggests favorability at higher temperatures. This could affect the conditions under which each step is carried out.
Combining the steps would require conditions that favor both reactions simultaneously, which may be challenging due to their differing entropy changes. Separate steps allow for optimization of conditions for each reaction.
Given the differing entropy changes and potential temperature requirements, it may be more practical to carry out the reactions in separate steps to optimize conditions for each reaction individually. This approach allows for better control over the production process.>

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Thermodynamics and Entropy

Thermodynamics is the study of energy transformations, and entropy (ΔS) is a measure of disorder in a system. In the context of chemical reactions, a negative ΔS indicates that the reaction leads to a decrease in disorder, while a positive ΔS suggests an increase. Understanding the entropy changes in the given reactions is crucial for predicting the feasibility and spontaneity of the processes involved in methanol and methane production.
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Entropy in Thermodynamics

Reaction Mechanism

A reaction mechanism outlines the step-by-step sequence of elementary reactions that lead to the overall chemical transformation. In this case, the production of methanol from CO and H2 occurs in two distinct steps. Analyzing whether to carry out these reactions separately or together requires understanding how the intermediate products behave and how they influence the overall efficiency and yield of the desired products.
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Reaction Mechanism Overview

Industrial Process Design

Industrial process design involves optimizing chemical reactions for large-scale production, considering factors like cost, efficiency, and safety. When deciding whether to conduct reactions in separate steps or in a continuous process, one must evaluate the energy requirements, potential for side reactions, and the economic implications of each approach. This decision impacts the overall productivity and sustainability of the methanol-to-methane conversion process.
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Spontaneity of Processes
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Domanda del libro di testo

Consider the unbalanced equation: I2(s) → I-(aq) + IO3-(aq) (d) What pH is required for the reaction to be at equilibrium at 25°C when [I-] = 0.10M and [IO3-] = 0.50 M?

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Domanda del libro di testo

Methanol (CH3OH) is made industrially in two steps from CO and H2. It is so cheap to make that it is being considered for use as a precursor to hydrocarbon fuels, such as methane (CH4):

Step 1. CO(g) + 2 H2(g) S CH3OH(l) ΔS° = - 332 J/K

Step 2. CH3OH1l2 → CH4(g) + 1/2 O2(g) ΔS° = 162 J/K

(k) Calculate an overall ΔG°, ΔH°, and ΔS° for the formation of CH4 from CO and H2.

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Domanda del libro di testo
For a process to be spontaneous, the total entropy of the system and its surroundings must increase; that is ΔStotal = ΔSsystem + ΔSsurr 7 0 for a spontaneous process Furthermore, the entropy change in the surroundings, ΔSsurr, is related to the enthalpy change for the process by the equa- tion ΔSsurr = - ΔH>T. (b) What is the value of ΔSsurr for the photosynthesis of glu- cose from CO2 at 298 K? 6 CO21g2 + 6 H2O1l2 S C6H12O61s2 + 6 O21g2 ΔG° = 2879 kJ ΔS° = - 262 J>K
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Domanda del libro di testo

Methanol (CH3OH) is made industrially in two steps from CO and H2. It is so cheap to make that it is being considered for use as a precursor to hydrocarbon fuels, such as methane (CH4):

Step 1. CO(g) + 2 H2(g) S CH3OH(l) ΔS° = - 332 J/K

Step 2. CH3OH1l2 → CH4(g) + 1/2 O2(g) ΔS° = 162 J/K

(l) Is the overall reaction spontaneous at 298 K?

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