Textbook Question
Calculate ΔSsurr at the indicated temperature for each reaction. d. ΔH°rxn = +114 kJ; 77 K
Ch.19 - Free Energy & Thermodynamics
Chapter 19, Problem 44a
Given the values of ΔH°rxn, ΔS°rxn, and T, determine ΔSuniv and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) a. ΔH°rxn = -75 kJ; ΔS°rxn = -127 J/K; T = 298 K
Verified step by step guidance1
Convert \( \Delta H^\circ_{rxn} \) from kJ to J by multiplying by 1000, since \( \Delta S^\circ_{rxn} \) is given in J/K.
Calculate \( \Delta S_{univ} \) using the formula: \( \Delta S_{univ} = \Delta S^\circ_{rxn} - \frac{\Delta H^\circ_{rxn}}{T} \).
Substitute the given values into the formula: \( \Delta S_{univ} = -127 \text{ J/K} - \frac{-75000 \text{ J}}{298 \text{ K}} \).
Simplify the expression to find \( \Delta S_{univ} \).
Determine the spontaneity of the reaction: if \( \Delta S_{univ} > 0 \), the reaction is spontaneous; if \( \Delta S_{univ} < 0 \), it is non-spontaneous.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Gibbs Free Energy
Gibbs Free Energy (G) is a thermodynamic potential that helps predict the spontaneity of a reaction at constant temperature and pressure. It is calculated using the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy. A negative ΔG indicates that a reaction is spontaneous, while a positive ΔG suggests it is non-spontaneous.
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Gibbs Free Energy of Reactions
Entropy (ΔS)
Entropy (ΔS) is a measure of the disorder or randomness in a system. In the context of chemical reactions, it quantifies the change in disorder as reactants transform into products. A positive ΔS indicates an increase in disorder, which generally favors spontaneity, while a negative ΔS suggests a decrease in disorder, which can hinder spontaneity.
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Enthalpy (ΔH)
Enthalpy (ΔH) is a measure of the total heat content of a system and reflects the energy changes during a chemical reaction. A negative ΔH indicates that the reaction is exothermic, releasing heat, which often contributes to spontaneity. Conversely, a positive ΔH indicates an endothermic reaction, absorbing heat, which may require a favorable entropy change to be spontaneous.
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Related Practice
Textbook Question
Given the values of ΔH°rxn, ΔS°rxn, and T, determine ΔSuniv and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) a. ΔH°rxn = +135 kJ; ΔS°rxn = -282 J/K; T = 298 K
Textbook Question
Given the values of ΔH°rxn, ΔS°rxn, and T, determine ΔSuniv and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) c. ΔH°rxn = -135 kJ; ΔS°rxn = -282 J>K; T = 298 K
Textbook Question
Given the values of ΔH°rxn, ΔS°rxn, and T, determine ΔSuniv and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) c. ΔH°rxn = +75 kJ; ΔS°rxn = -127 J/K; T = 298 K
Textbook Question
Calculate the change in Gibbs free energy for each of the sets of ΔH°rxn, ΔS°rxn, and T given in Problem 44. 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.) 2 Ca(s) + O2( g) → 2 CaO(s) ΔH°rxn = -1269.8 kJ; ΔS°rxn = -364.6 J/K
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