For a certain chemical reaction, ΔH° = -35.4 kJ and ΔS° = -85.5 J/K. (b) Does the reaction lead to an increase or decrease in the randomness or disorder of the system?
Ch.19 - Chemical Thermodynamics

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Capitolo 19, Problema 53b
(b) For a certain process that occurs at constant T and P, the value of ΔG is positive. Is the process spontaneous?
Guida verificata passo dopo passo1
Understand the concept of Gibbs Free Energy (ΔG): Gibbs Free Energy is a thermodynamic potential that can be used to predict the spontaneity of a process at constant temperature and pressure.
Recall the spontaneity criterion: A process is spontaneous if the change in Gibbs Free Energy (ΔG) is negative. If ΔG is positive, the process is non-spontaneous under the given conditions.
Analyze the given condition: The problem states that ΔG is positive for the process occurring at constant temperature and pressure.
Apply the spontaneity criterion to the given condition: Since ΔG is positive, according to the criterion, the process is not spontaneous.
Conclude based on the analysis: The process is non-spontaneous at constant temperature and pressure because the value of ΔG is positive.

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Gibbs Free Energy (ΔG)
Gibbs Free Energy (ΔG) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. A negative ΔG indicates that a process can occur spontaneously, while a positive ΔG suggests that the process is non-spontaneous under the given conditions.
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Gibbs Free Energy of Reactions
Spontaneity of Reactions
The spontaneity of a reaction refers to its ability to proceed without external intervention. A spontaneous process is characterized by a decrease in free energy (ΔG < 0), meaning it can occur naturally. Conversely, if ΔG is positive, the process is not spontaneous and requires energy input to occur.
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Spontaneity of Processes
Thermodynamic Equilibrium
Thermodynamic equilibrium is the state of a system where macroscopic properties are uniform and do not change over time. At equilibrium, the Gibbs Free Energy is at a minimum, and any process that would increase ΔG is not spontaneous. A positive ΔG indicates that the system is not at equilibrium and will not proceed spontaneously in the forward direction.
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First Law of Thermodynamics
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For a certain chemical reaction, ΔH° = -35.4 kJ and ΔS° = -85.5 J/K. (c) Calculate ΔG° for the reaction at 298 K. (d) Is the reaction spontaneous at 298 K under standard conditions?
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