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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 143l
Capitolo 18, Problema 143l

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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Calculate the overall change in entropy (\(\Delta S^\circ_{\text{total}}\)) for the reaction by adding the \(\Delta S^\circ\) values for each step: \(\Delta S^\circ_{\text{total}} = \Delta S^\circ_{\text{Step 1}} + \Delta S^\circ_{\text{Step 2}}\).
Determine the change in enthalpy (\(\Delta H^\circ\)) for each step if provided, or use standard enthalpy values to calculate it.
Use the Gibbs free energy equation \(\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ\) to find the overall \(\Delta G^\circ\) at 298 K.
Evaluate the sign of \(\Delta G^\circ\): if \(\Delta G^\circ < 0\), the reaction is spontaneous; if \(\Delta G^\circ > 0\), it is non-spontaneous.
Conclude whether the overall reaction is spontaneous at 298 K based on the sign of \(\Delta G^\circ\).

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Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict the spontaneity of a reaction at constant temperature and pressure. A reaction is spontaneous if the change in Gibbs Free Energy (ΔG) is negative. It is calculated using the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.
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Gibbs Free Energy of Reactions

Entropy (ΔS)

Entropy (S) is a measure of the disorder or randomness in a system. The change in entropy (ΔS) during a reaction indicates how the distribution of energy changes. A positive ΔS suggests an increase in disorder, while a negative ΔS indicates a decrease. In the context of the given reactions, the values of ΔS will influence the spontaneity of the overall process.
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Entropy in Thermodynamics

Spontaneity of Reactions

The spontaneity of a chemical reaction refers to its ability to proceed without external intervention. It is determined by the balance between enthalpy (ΔH) and entropy (ΔS) changes. A reaction is spontaneous if the overall ΔG is negative, which can occur when the enthalpy decrease outweighs the entropy decrease, or vice versa, depending on the temperature and the magnitudes of ΔH and ΔS.
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Spontaneity of Processes
Pratica correlata
Domanda del libro di testo

Consider the unbalanced equation: (b) Use the data in Appendix B and ΔG°f for IO3-(aq)= -128.0 kJ/mol to calculate ΔG° for the reaction at 25 °C.

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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?

317
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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.

365
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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

(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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