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Ch.9 - Thermochemistry: Chemical Energy
All textbooksMcMurry 8th EditionCh.9 - Thermochemistry: Chemical EnergyProblem 123
Chapter 9, Problem 123

What are the two terms that make up the free-energy change for a reaction, ΔG, and which of the two is usually more important?

Verified step by step guidance
1
Step 1: Understand that the free-energy change for a reaction, denoted as ΔG, is a thermodynamic quantity that predicts the direction of a chemical reaction and its spontaneity.
Step 2: Recognize that ΔG is composed of two main terms: the enthalpy change (ΔH) and the entropy change (ΔS), which are related by the equation ΔG = ΔH - TΔS, where T is the temperature in Kelvin.
Step 3: The enthalpy change (ΔH) represents the heat absorbed or released during a reaction at constant pressure. It indicates whether a reaction is exothermic (releases heat) or endothermic (absorbs heat).
Step 4: The entropy change (ΔS) measures the change in disorder or randomness of the system. A positive ΔS indicates an increase in disorder, while a negative ΔS indicates a decrease.
Step 5: Consider that the relative importance of ΔH and TΔS depends on the specific reaction and conditions, but generally, at lower temperatures, ΔH tends to be more significant, while at higher temperatures, TΔS can become more influential.
Related Practice
Textbook Question
Isooctane, C8H18, is the component of gasoline from which the term octane rating derives (b) The standard molar heat of combustion of isooctane (l) is -5461 kJ/mol. Calculate ΔH°f for isooctane(l)
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Textbook Question

Isooctane, C8H18, is the component of gasoline from which the term octane rating derives. (a) Write a balanced equation for the combustion of isooctane(l) with O2 to yield CO2(g) and H2O(l)

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Textbook Question

What does entropy measure?

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Textbook Question

How is it possible for a reaction to be spontaneous yet endothermic?

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Textbook Question

Tell whether the free-energy changes, ΔG, for the processes listed in Problem 9.127 are likely to be positive, negative, or zero.

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Open Question
When a bottle of perfume is opened, odorous molecules mix with air and slowly diffuse throughout the entire room. Is ΔG for the diffusion process positive, negative, or zero? What about ΔH and ΔS for the diffusion?