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Ch.19 - Chemical Thermodynamics
Brown - Chemistry: The Central Science 14th Edition
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Tutti i libri di testoBrown 14th EditionCh.19 - Chemical ThermodynamicsProblema 12
Capitolo 19, Problema 12

Which of the following processes are spontaneous?
a. the melting of ice cubes at −10 °C and 1 atm pressure
b. separating a mixture of N2 and O2 into two separate samples, one that is pure N2 and one that is pure O2
c. alignment of iron filings in a magnetic field
d. the reaction of hydrogen gas with oxygen gas to form water vapor at room temperature
e. the dissolution of HCl(g) in water to form concentrated hydrochloric acid

Guida verificata passo dopo passo
1
Step 1: Understand the concept of spontaneity in chemical processes. A spontaneous process is one that occurs naturally under given conditions without needing external energy input. It is often associated with an increase in entropy or a decrease in free energy.
Step 2: Analyze option (a): The melting of ice cubes at -10 °C and 1 atm pressure. Consider the phase change and the temperature. Ice melts spontaneously at temperatures above 0 °C, so at -10 °C, this process is not spontaneous.
Step 3: Analyze option (b): Separating a mixture of N2 and O2 into pure samples. This process decreases entropy because it involves creating order from disorder, which is not spontaneous without external work.
Step 4: Analyze option (c): Alignment of iron filings in a magnetic field. This process is spontaneous because the magnetic field provides the necessary energy to align the filings, and it occurs naturally when the filings are exposed to the field.
Step 5: Analyze option (d) and (e): The reaction of hydrogen gas with oxygen gas to form water vapor is spontaneous at room temperature due to the release of energy (exothermic reaction). The dissolution of HCl(g) in water is also spontaneous as it involves the release of energy and an increase in entropy.

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Spontaneity in Chemical Processes

A spontaneous process is one that occurs without the need for external energy input. It is driven by the increase in the system's entropy or the decrease in its Gibbs free energy. Understanding spontaneity helps predict whether a reaction or physical change will occur under given conditions.
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Spontaneity of Processes

Entropy and Temperature

Entropy is a measure of the disorder or randomness in a system. As temperature increases, the entropy of a system typically increases, which can influence the spontaneity of processes. For example, the melting of ice at higher temperatures is spontaneous due to increased molecular motion and disorder.
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Entropy and Physical Changes

Gibbs Free Energy

Gibbs free energy (G) combines enthalpy and entropy to determine the spontaneity of a process at constant temperature and pressure. A negative change in Gibbs free energy (ΔG < 0) indicates a spontaneous process, while a positive change (ΔG > 0) suggests non-spontaneity. This concept is crucial for evaluating chemical reactions and physical changes.
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Gibbs Free Energy of Reactions
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