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Ch.9 - Thermochemistry: Chemical Energy
All textbooksMcMurry 8th EditionCh.9 - Thermochemistry: Chemical EnergyProblem 14
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Chapter 9, Problem 14

The boiling point of a substance is defined as the temperature at which liquid and vapor coexist in equilibrium. Use the heat of vaporization ΔHvap = 30.91 kJ/mol and the entropy of vaporization ΔSvap = 93.2 J/K·mol to calculate the boiling point (°C) of liquid bromine.

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1
Step 1: Understand the relationship between the boiling point, heat of vaporization (ΔHvap), and entropy of vaporization (ΔSvap). At the boiling point, the Gibbs free energy change (ΔG) for the phase transition is zero.
Step 2: Use the Gibbs free energy equation for phase transitions: ΔG = ΔHvap - TΔSvap. Set ΔG to zero because at the boiling point, the liquid and vapor are in equilibrium.
Step 3: Rearrange the equation to solve for the temperature (T): T = ΔHvap / ΔSvap.
Step 4: Convert the units of ΔHvap from kJ/mol to J/mol to match the units of ΔSvap. (1 kJ = 1000 J)
Step 5: Substitute the values of ΔHvap and ΔSvap into the equation to calculate the temperature in Kelvin, then convert the temperature from Kelvin to Celsius by subtracting 273.15.
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Related Practice
Textbook Question
Calculate the enthalpy change for the reaction C(s) + 2 H2(g) → CH4(g) ΔH = ? Given the enthalpy values for the following reactions CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l) ΔH = −890.4 kJ C(s) + O2(g) → CO2(g) ΔH = −393.5 kJ H2(g) + 1/2 O2(g) → H2O (g) ΔH = −285.8 kJ (a) −1569.7 kJ (b) +211.1 kJ (c) −1855.5 kJ (d) −74.7 kJ
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Textbook Question
A table of standard enthalpies of formation (ΔH°f) gives a value of −467.9 kJ/mol for NaNO3(s). Which reaction has a ΔH° value of −467.9 kJ? (a) Na+ (aq) + NO3−(aq) → NaNO3(s) (b) Na(s) + N(g + O3(g) → NaNO3(s) (c) Na(s) + 1/2 N2(g) + 3/2 O2(g) → NaNO3(s) (d) 2 Na(s) + N2(g) + 3 O2(g) → 2 NaNO3(s)
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Textbook Question
What is ΔH for the explosion of nitroglycerin? (LO 9.14) 2 C3H5(NO3)3(l) → 3 N2(g) + 1/2 O2(g) + 6 CO2(g) + 5 H2O(g) (a) −315.0 kJ (b) −4517 kJ (c) −3425 kJ (d) −3062 kJ
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Open Question
Consider the following endothermic reaction of gaseous AB3 molecules with A2 molecules (LO 9.16, 9.17). Identify the true statement about the spontaneity of the reaction. (a) The reaction is likely to be spontaneous at high temperatures. (b) The reaction is likely to be spontaneous at low temperatures. (c) The reaction is always spontaneous. (d) The reaction is never spontaneous.
Textbook Question
A piece of dry ice (solid CO2) is placed inside a balloon, and the balloon is tied shut. Over time, the carbon dioxide sub- limes, causing the balloon to increase in volume. Give the sign of the enthalpy change and the sign of work for the sublima- tion of CO2.
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Textbook Question

Imagine a reaction that results in a change in both volume and temperature: (a) Has any work been done? If so, is its sign positive or negative?

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