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Ch.9 - Thermochemistry: Chemical Energy
All textbooksMcMurry 8th EditionCh.9 - Thermochemistry: Chemical EnergyProblem 135
Chapter 9, Problem 135

9.135 Suppose that a reaction has ΔH = + 41 kJ and ΔS = - 27 J/K. At what temperature, if any, will it change between spontaneous and nonspontaneous?

Verified step by step guidance
1
Step 1: Understand the relationship between Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) using the equation ΔG = ΔH - TΔS, where T is the temperature in Kelvin.
Step 2: Recognize that a reaction changes from spontaneous to nonspontaneous when ΔG = 0. This is the condition for equilibrium.
Step 3: Set the equation ΔG = ΔH - TΔS to zero and solve for the temperature T. This gives T = ΔH / ΔS.
Step 4: Convert the units of ΔS from J/K to kJ/K to match the units of ΔH. Since 1 kJ = 1000 J, divide ΔS by 1000.
Step 5: Substitute the values of ΔH and the converted ΔS into the equation T = ΔH / ΔS to find the temperature at which the reaction changes between spontaneous and nonspontaneous.
Related Practice
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?
Open Question
Tell whether reactions with the following values of ΔH and ΔS are spontaneous or nonspontaneous and whether they are exothermic or endothermic. (a) ΔH = -128 kJ; ΔS = 35 J/K at 500 K (b) ΔH = +67 kJ; ΔS = -140 J/K at 250 K (c) ΔH = +75 kJ; ΔS = 95 J/K at 800 K
Open Question
Which of the reactions (a)–(d) in Problem 9.132 are spontaneous at all temperatures, which are nonspontaneous at all temperatures, and which have an equilibrium temperature?
Textbook Question
(d) What is the kinetic energy of an electron traveling at velocity (c)?
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Textbook Question

Ethyl alcohol has ΔHfusion = 5.02 kJ/mol and melts at - 114.1 °C. What is the value of ΔSfusion for ethyl alcohol?

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