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Ch.18 - Free Energy and Thermodynamics
Chapter 18, Problem 61d

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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Key Concepts

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

Thermodynamic Functions (ΔH, ΔS, ΔG)

ΔH°rxn represents the change in enthalpy, indicating the heat absorbed or released during a reaction. ΔS°rxn denotes the change in entropy, reflecting the disorder or randomness of the system. ΔG°rxn, the Gibbs free energy change, determines the spontaneity of a reaction; a negative ΔG indicates spontaneity at constant temperature and pressure.
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Spontaneity of Reactions

A reaction is spontaneous if it occurs without external intervention, which is determined by the sign of ΔG°rxn. If ΔG°rxn is negative, the reaction is spontaneous; if positive, it is non-spontaneous. The relationship between ΔH, ΔS, and temperature (T) is crucial, as it can influence the spontaneity of a reaction under different conditions.
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Temperature's Effect on Spontaneity

The temperature can affect the spontaneity of a reaction through the Gibbs free energy equation: ΔG°rxn = ΔH°rxn - TΔS°rxn. If ΔS°rxn is positive, increasing temperature can make a non-spontaneous reaction spontaneous. Conversely, if ΔS°rxn is negative, lowering the temperature may be necessary to achieve spontaneity.
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Related Practice
Textbook Question

In photosynthesis, plants form glucose (C6H12O6) and oxygen from carbon dioxide and water. Write a balanced equation for photosynthesis and calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C. Is photosynthesis spontaneous?

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Open Question
For each reaction, calculate ΔH°rxn, ΔS°rxn, and ΔG°rxn at 25 °C and state whether 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? b. NH4Cl(s) → HCl(g) + NH3(g) c. 3 H2(g) + Fe2O3(s) → 2 Fe(s) + 3 H2O(g)
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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Open Question
For each reaction, calculate ΔH°_rxn, ΔS°_rxn, and ΔG°_rxn at 25°C and determine whether the reaction is spontaneous. If the reaction is not spontaneous, could a change in temperature make it spontaneous? If so, should the temperature be increased or decreased from 25°C? b. 2 NH3(g) → N2H4(g) + H2(g)
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? c. N2(g) + O2(g) → 2 NO(g)

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