For each reaction, calculate ΔH°_rxn, ΔS°_rxn, and ΔG°_rxnat 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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Identify the standard enthalpy change (ΔH°) and standard entropy change (ΔS°) for the reaction using standard enthalpies and entropies of formation for each compound.

Calculate the standard enthalpy change of the reaction (ΔH°rxn) using the formula: ΔH°rxn = ΣΔH°f(products) - ΣΔH°f(reactants).

Calculate the standard entropy change of the reaction (ΔS°rxn) using the formula: ΔS°rxn = ΣS°(products) - ΣS°(reactants).

Calculate the standard Gibbs free energy change (ΔG°rxn) using the formula: ΔG°rxn = ΔH°rxn - TΔS°rxn, where T is the temperature in Kelvin (298 K for 25 °C).

Determine the spontaneity of the reaction: if ΔG°rxn < 0, the reaction is spontaneous; if ΔG°rxn > 0, the reaction is non-spontaneous. If non-spontaneous, analyze the signs of ΔH°rxn and ΔS°rxn to decide if changing the temperature could make the reaction spontaneous.

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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° (enthalpy change), ΔS° (entropy change), and ΔG° (Gibbs free energy change) are fundamental thermodynamic functions used to assess the energy and disorder changes in a chemical reaction. ΔH° indicates whether a reaction is exothermic or endothermic, while ΔS° reflects the change in disorder. ΔG° combines these two to determine spontaneity; a negative ΔG° indicates a spontaneous reaction at a given temperature.

Spontaneity of Reactions

A reaction is considered spontaneous if it occurs without external intervention, which is determined by the sign of ΔG°. If ΔG° is negative, the reaction is spontaneous; if positive, it is non-spontaneous. The spontaneity can also depend on temperature, as the relationship between ΔH°, ΔS°, and ΔG° is temperature-dependent, described by the equation ΔG° = ΔH° - TΔS°.

Temperature's Effect on Spontaneity

The temperature can influence the spontaneity of a reaction, particularly when ΔH° and ΔS° have opposing signs. If ΔS° is positive (increased disorder) and ΔH° is positive (endothermic), raising the temperature can make ΔG° negative, thus making the reaction spontaneous. Conversely, if ΔS° is negative (decreased disorder) and ΔH° is negative (exothermic), lowering the temperature may be necessary for spontaneity.

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Methanol (CH₃OH) burns in oxygen to form carbon dioxide and water. Write a balanced equation for the combustion of liquid methanol and calculate ΔH°_rxn, ΔS°_rxn, and ΔG°_rxnat 25 °C. Is the combustion of methanol spontaneous?

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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°_rxnat 25 °C. Is photosynthesis spontaneous?

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Textbook Question

For each reaction, calculate ΔH°_rxn, ΔS°_rxn, and ΔG°_rxnat 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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