Brown - Chemistry: The Central Science 14th Edition

Ch.19 - Chemical Thermodynamics

Back

All textbooks

Brown 14th Edition

Ch.19 - Chemical Thermodynamics

Problem 102
The potassium-ion concentration in blood plasma is about 5.0⨉10^-3 M, whereas the concentration in muscle-cell fluid is much greater (0.15 M ). The plasma and intracellular fluid are separated by the cell membrane, which we assume is permeable only to K⁺. (a) What is ΔG for the transfer of 1 mol of K⁺ from blood plasma to the cellular fluid at body temperature 37 °C? (b) What is the minimum amount of work that must be used to transfer this K⁺?

Problem 103

Most liquids follow Trouton’s rule (see Exercise 19.93), which states that the molar entropy of vaporization is approximately 88 J/mol⋅K. The normal boiling points and enthalpies of vaporization of several organic liquids are as follows: (b) With reference to intermolecular forces (Section 11.2), can you explain any exceptions to the rule? (c) Would you expect water to obey Trouton’s rule? By using data in Appendix B, check the accuracy of your conclusion.

Problem 104

In chemical kinetics, the entropy of activation is the entropy change for the process in which the reactants reach the activated complex. Predict whether the entropy of activation for a bimolecular process is usually positive or negative.

Problem 105

At what temperatures is the following reaction, the reduction of magnetite by graphite to elemental iron, spontaneous? Fe₃O₄(s) + 2 C(s, graphite) → 2 CO₂(g) + 3 Fe(s)

Problem 106

The following processes were all discussed in Chapter 18, “Chemistry of the Environment.” Estimate whether the entropy of the system increases or decreases during each process: (a) photodissociation of O₂(g). (b) formation of ozone from oxygen molecules and oxygen atoms. (c) diffusion of CFCs into the stratosphere. (d) desalination of water by reverse osmosis.

Problem 107

An ice cube with a mass of 20 g at -20 °C (typical freezer temperature) is dropped into a cup that holds 500 mL of hot water, initially at 83 °C. What is the final temperature in the cup? The density of liquid water is 1.00 g>mL; the specific heat capacity of ice is 2.03 J>g@C; the specific heat capacity of liquid water is 4.184 J>g@C; the enthalpy of fusion of water is 6.01 kJ>mol.

Problem 108

Carbon disulfide 1CS22 is a toxic, highly flammable substance. The following thermodynamic data are available for CS21l2 and CS21g2 at 298 K:

(e) Use the data in the table to calculate ΔS° at 298 K for the vaporization of CS21l2. Is the sign of ΔS° as you would expect for a vaporization?

Problem 109

The following data compare the standard enthalpies and free energies of formation of some crystalline ionic substances and aqueous solutions of the substances:

(a) Write the formation reaction for AgNO31s2. Based on this reaction, do you expect the entropy of the system to increase or decrease upon the formation of AgNO31s2? (b) Use ΔH°f and ΔG°f of AgNO31s2 to determine the entropy change upon formation of the substance. Is your answer consistent with your reasoning in part (a)?

Problem 110a

Consider the following equilibrium: N₂O₄(g) ⇌ 2 NO₂(g) Thermodynamic data on these gases are given in Appendix C. You may assume that ΔH° and ΔS° do not vary with temperature. (a) At what temperature will an equilibrium mixture contain equal amounts of the two gases?

Problem 111a,c

The reaction SO₂(g) + 2 H₂S(g) ⇌ 3 S(s) + 2 H₂O(g) is the basis of a suggested method for removal of SO2 from power-plant stack gases. The standard free energy of each substance is given in Appendix C. (a) What is the equilibrium constant for the reaction at 298 K? (c) If P_SO2 = P_H2S and the vapor pressure of water is 25 torr, calculate the equilibrium SO₂ pressure in the system at 298 K.

Problem 111b

The reaction SO₂(g) + 2 H₂S(g) ⇌ 3 S(s) + 2 H₂O(g) is the basis of a suggested method for removal of SO₂ from power-plant stack gases. The standard free energy of each substance is given in Appendix C. (b) In principle, is this reaction a feasible method of removing SO₂?

Problem 111d

The reaction SO₂(g) + 2 H₂S(g) ⇌ 3 S(s) + 2 H₂O(g) is the basis of a suggested method for removal of SO₂ from power-plant stack gases. The standard free energy of each substance is given in Appendix C. (d) Would you expect the process to be more or less effective at higher temperatures?

Problem 112a

When most elastomeric polymers (e.g., a rubber band) are stretched, the molecules become more ordered, as illustrated here:

Suppose you stretch a rubber band. (a) Do you expect the entropy of the system to increase or decrease?

Problem 115

Hydrogen gas has the potential for use as a clean fuel in reaction with oxygen. The relevant reaction is 2 H21g2 + O21g2 ¡ 2 H2O1l2 Consider two possible ways of utilizing this reaction as an electrical energy source: (i) Hydrogen and oxygen gases are combusted and used to drive a generator, much as coal is currently used in the electric power industry; (ii) hydrogen and oxygen gases are used to generate electricity directly by using fuel cells that operate at 85 °C. (a) Use data in Appendix C to calculate ∆H° and ∆S° for the reaction. We will assume that these values do not change appreciably with temperature.

Problem 102