Fill in the blanks in the table. Both ΔH and ΔS refer to the system.

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Identify the given values in the problem, such as \( \Delta H \) (enthalpy change) and \( \Delta S \) (entropy change) for the system.

Recall the relationship between \( \Delta G \) (Gibbs free energy change), \( \Delta H \), and \( \Delta S \) using the equation: \( \Delta G = \Delta H - T \Delta S \), where \( T \) is the temperature in Kelvin.

Determine if any additional information is provided, such as temperature or specific conditions, to calculate the missing values.

Use the equation \( \Delta G = \Delta H - T \Delta S \) to solve for the missing variable, ensuring all units are consistent (e.g., converting \( \Delta S \) from J/mol·K to kJ/mol·K if necessary).

Check your work by verifying that the calculated values make sense in the context of the problem, such as ensuring that the signs of \( \Delta H \) and \( \Delta S \) align with the expected spontaneity of the reaction.

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Key Concepts

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

Enthalpy (ΔH)

Enthalpy (ΔH) is a thermodynamic quantity that represents the total heat content of a system. It reflects the energy required to create a system at constant pressure and is crucial for understanding heat transfer during chemical reactions. A positive ΔH indicates an endothermic process, while a negative ΔH signifies an exothermic reaction.

Entropy (ΔS)

Entropy (ΔS) is a measure of the disorder or randomness in a system. It quantifies the number of ways a system can be arranged, with higher entropy indicating greater disorder. In thermodynamics, changes in entropy help predict the spontaneity of a process; a positive ΔS often favors spontaneity, while a negative ΔS may hinder it.

Gibbs Free Energy (ΔG)

Gibbs Free Energy (ΔG) combines enthalpy and entropy to determine the spontaneity of a process at constant temperature and pressure. The relationship is given by the equation ΔG = ΔH - TΔS, where T is the temperature in Kelvin. A negative ΔG indicates a spontaneous process, while a positive ΔG suggests non-spontaneity.

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Gibbs Free Energy of Reactions

Related Practice

Textbook Question

Calculate the change in Gibbs free energy for each of the sets of ΔH_rxn, ΔS_rxn, and T given in Problem 42. Predict whether or not each reaction is spontaneous at the temperature indicated. (Assume that all reactants and products are in their standard states.)

Textbook Question

Calculate the free energy change for this reaction at 25 °C. Is the reaction spontaneous? (Assume that all reactants and products are in their standard states.) C₃H₈(g) + 5 O₂(g) → 3 CO₂(g) + 4 H₂O(g) ΔH°_rxn= -2217 kJ; ΔS°_rxn = 101.1 J/K

Textbook Question

Calculate the free energy change for this reaction at 25 °C. Is the reaction spontaneous? (Assume that all reactants and products are in their standard states.) 2 Ca(s) + O₂( g) → 2 CaO(s) ΔH°_rxn = -1269.8 kJ; ΔS°_rxn = -364.6 J/K

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Textbook Question

Predict the conditions (high temperature, low temperature, all temperatures, or no temperatures) under which each reaction is spontaneous. a. H₂O(g) → H₂O(l) b. CO₂(s) → CO₂(g) c. H₂(g) → 2 H(g) d. 2 NO₂(g) → 2 NO(g) + O₂(g) (endothermic)

Textbook Question

How does the molar entropy of a substance change with increasing temperature?

Textbook Question

For each pair of substances, choose the one that you expect to have the higher standard molar entropy (S°) at 25 °C. Explain your choices. a. CO(g); CO₂(g) b. CH₃OH(l); CH₃OH(g) c. Ar(g); CO₂(g) d. CH₄(g); SiH₄(g) e. NO₂(g); CH₃CH₂CH₃(g) f. NaBr(s); NaBr(aq)