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Ch.19 - Free Energy & Thermodynamics
Chapter 19, Problem 62c

For each reaction, calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C and state whether or not the reaction is spontaneous. If the reaction is not spontaneous, would a change in temperature make it spontaneous? If so, should the temperature be raised or lowered from 25 °C? c. N2(g) + O2(g) → 2 NO(g)

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Enthalpy (ΔH°rxn)

Enthalpy change (ΔH°rxn) is the heat absorbed or released during a chemical reaction at constant pressure. It indicates whether a reaction is exothermic (releases heat, ΔH° < 0) or endothermic (absorbs heat, ΔH° > 0). This value is crucial for determining the energy dynamics of the reaction and influences its spontaneity.
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Entropy (ΔS°rxn)

Entropy change (ΔS°rxn) measures the disorder or randomness of a system during a reaction. A positive ΔS° indicates an increase in disorder, while a negative ΔS° suggests a decrease. Entropy is a key factor in assessing the spontaneity of a reaction, as reactions tend to favor states of higher entropy.
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Gibbs Free Energy (ΔG°rxn)

Gibbs Free Energy change (ΔG°rxn) combines enthalpy and entropy to determine the spontaneity of a reaction at constant temperature and pressure. It is calculated using the equation ΔG° = ΔH° - TΔS°. A negative ΔG° indicates a spontaneous reaction, while a positive ΔG° suggests non-spontaneity. The temperature's effect on spontaneity can be analyzed through this relationship.
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Related Practice
Textbook Question

For each reaction, calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C and state whether or not the reaction is spontaneous. If the reaction is not spontaneous, would a change in temperature make it spontaneous? If so, should the temperature be raised or lowered from 25 °C? a. N2O4(g) → 2 NO2(g)

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Textbook Question

For each reaction, calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C and state whether or not the reaction is spontaneous. If the reaction is not spontaneous, would a change in temperature make it spontaneous? If so, should the temperature be raised or lowered from 25 °C? d. N2(g) + 3 H2(g) → 2 NH3(g)

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Textbook Question

For each reaction, calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C and state whether or not the reaction is spontaneous. If the reaction is not spontaneous, would a change in temperature make it spontaneous? If so, should the temperature be raised or lowered from 25 °C? a. 2 CH4(g) → C2H6(g) + H2(g)

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Textbook Question

For each reaction, calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C and state whether or not the reaction is spontaneous. If the reaction is not spontaneous, would a change in temperature make it spontaneous? If so, should the temperature be raised or lowered from 25 °C? d. 2 KClO3(s) → 2 KCl(s) + 3 O2(g)

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Textbook Question

Use standard free energies of formation to calculate ΔG° at 25 °C for each reaction in Problem 61. How do the values of ΔG° calculated this way compare to those calculated from ΔH° and ΔS°? Which of the two methods could be used to determine how ΔG° changes with temperature?

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Textbook Question

Consider the reaction: 2 NO(g) + O2(g) → 2 NO2(g) Estimate ΔG° for this reaction at each temperature and predict whether or not the reaction is spontaneous. (Assume that ΔH° and ΔS° do not change too much within the given temperature range.) b. 715 K

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