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

Given the values of ΔH°_rxn, ΔS°_rxn, and T, determine ΔS_univ and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) a. ΔH°_rxn = -95 kJ; ΔS°_rxn = -157 J/K; T = 298 K

Textbook Question

Given the values of ΔH°_rxn, ΔS°_rxn, and T, determine ΔS_univ and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) c. ΔH°_rxn = +95 kJ; ΔS°_rxn = -157 J/K; T = 298 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)