19. Chemical Thermodynamics

Which of the following statements is/are true?

a) The rusting of iron by oxygen is a non-spontaneous reaction.

b) The addition of a catalyst to a reaction increases spontaneity.

c) The movement of heat from a cold object to a hot object is a non-spontaneous reaction.

d) The diffusion of perfume molecules from one side of a room to the other is a non-spontaneous reaction.

e) None of the above. 

Which of the following is (are) spontaneous processes?

(i) a ball rolling down a hill
(ii) a car rusting
(iii) the decomposition of water into H₂ gas and O₂ gas

A positive ΔS_system indicates what about the overall spontaneity of a process?

A process is always spontaneous under which conditions?

Which of the following is a true statement about the relationship between ΔG and K?

At what temperature does the following reaction become nonspontaneous?

2 NO (g) + O₂ (g) → 2 NO₂ (g)

Which of the following would have a negative ΔS?

Which of the following is a true statement about ΔS_surroundings?

Calculate ΔS_surr (in units of J/K) for the process in which 2.00 mol of water are placed into a freezer at −10.0℃.

Calculate ΔS°_rxn (J/K) for the formation reaction of the salt MgO (s).

The accompanying diagram shows how entropy varies with temperature for a substance that is a gas at the highest temperature shown. (c) If this substance is a perfect crystal at T = 0 K, what is the value of S at this temperature?

Which of the following processes are spontaneous and which are nonspontaneous: (d) lightning

Which of the following processes are spontaneous and which are nonspontaneous: (e) formation of CH4 and O2 molecules from CO2 and H2O at room temperature and 1 atm of pressure?

Which of the following processes are spontaneous and which are nonspontaneous: (a) the ripening of a banana

Indicate whether each statement is true or false. (a) A reaction that is spontaneous in one direction will be nonspontaneous in the reverse direction under the same reaction conditions. (b) All spontaneous processes are fast. (c) Most spontaneous processes are reversible. (d) An isothermal process is one in which the system loses no heat. (e) The maximum amount of work can be accomplished by an irreversible process rather than a reversible one.

Consider the vaporization of liquid water to steam at a pressure of 1 atm. (c) In what temperature range is it a nonspontaneous process?

The normal boiling point of Br21l2 is 58.8 °C, and its molar enthalpy of vaporization is ΔHvap = 29.6 kJ>mol. (b) Calculate the value of ΔS when 1.00 mol of Br21l2 is vaporized at 58.8 °C.

The element gallium (Ga) freezes at 29.8 °C, and its molar enthalpy of fusion is ΔHfus = 5.59 kJ>mol. (b) Calculate the value of ΔS when 60.0 g of Ga(l) solidifies at 29.8 °C.

Which of these processes is spontaneous? a. the combustion of natural gas b. the extraction of iron metal from iron ore c. a hot drink cooling to room temperature d. drawing heat energy from the ocean's surface to power a ship

Which of these processes are nonspontaneous? Are the nonspontaneous processes impossible? a. a bike going up a hill b. a meteor falling to Earth c. obtaining hydrogen gas from liquid water d. a ball rolling down a hill

(c) In a particular spontaneous process, the number of microstates available to the system decreases. What can you conclude about the sign of ΔSsurr?

(b) As a system goes from state A to state B, its entropy decreases. What can you say about the number of microstates corresponding to each state?

(a) What is the difference between a state and a microstate of a system?

Would each of the following changes increase, decrease, or have no effect on the number of microstates available to a system: (b) decrease in volume

Calculate the change in entropy that occurs in the system when 1.00 mole of diethyl ether (C4H10O) condenses from a gas to a liquid at its normal boiling point (34.6 °C). See Table 11.7 for heats of vaporization.

Which of the following processes are spontaneous, and which are nonspontaneous? (a) Freezing of water at 2 °C (b) Corrosion of iron metal (c) Expansion of a gas to fill the available volume (d) Separation of an unsaturated aqueous solution of potassium chloride into solid KCl and liquid water

Indicate whether each statement is true or false. (a) Unlike enthalpy, where we can only ever know changes in H, we can know absolute values of S. (b) If you heat a gas such as CO2, you will increase its degrees of translational, rotational and vibrational motions. (c) CO21g2 and Ar(g) have nearly the same molar mass. At a given temperature, they will have the same number of microstates.

Calculate ΔS surr at the indicated temperature for each reaction. d. ΔHrxn ° = +114 kJ; 77 K

Naphthalene, better known as 'mothballs,' has bp = 218 °C and ΔHvap = 43.3 k# J>mol. What is the entropy of vaporiza tion, ΔSvap in J>1K mol2 for naphthalene?

When rolling a pair of dice, there are two ways to get a point total of 3(1+2;2+1) but only one way to get a point total of 2(1+1). How many ways are there of getting point totals of 4 to 12? What is the most probable point total?

Consider the distribution of ideal gas molecules among three bulbs (A, B, and C) of equal volume. For each of the follow-ing states, determine the number of ways (W) that the state can be achieved, and use Boltzmann's equation to calculate the entropy of the state. (a) 2 molecules in bulb A (b) 2 molecules randomly distributed among bulbs A, B, and C

Make a rough, qualitative plot of the standard molar entropy versus temperature for methane from 0 K to 298 K. Incorporate the following data into your plot: mp = -182 °C; bp = -164 °C; °S = 186.2 J/(K*mol) at 25 °C.

For the vaporization of benzene, ∆Hvap = 30.7 kJ/mol and ∆Svap = 87.0 J/(K*mol). Does benzene boil at 70 °C and 1 atm pressure? Calculate the normal boiling point of benzene.

For the melting point of sodium chloride, ΔHfusion = 28.16 kJ/mol and ΔSfusion = 26.22 J/(K·mol). Does NaCl melt at 1100 K? Calculate the melting point of NaCl.

Consider a system that consists of two standard playing dice, with the state of the system defined by the sum of the values shown on the top faces. (f) Calculate the absolute entropy of the two-dice system.

A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH2F2. An air-conditioner refrigerant has the property that it readily vaporizes at atmospheric pressure and is easily compressed to its liquid phase under increased pressure. The operation of an air conditioner can be thought of as a closed system made up of the refrigerant going through the two stages shown here (the air circulation is not shown in this diagram).

During expansion, the liquid refrigerant is released into an expansion chamber at low pressure, where it vaporizes. The vapor then undergoes compression at high pressure back to its liquid phase in a compression chamber. (e) Suppose that a house and its exterior are both initially at 31 °C. Some time after the air conditioner is turned on, the house is cooled to 24 °C. Is this process spontaneous or nonspontaneous?

Trouton's rule states that for many liquids at their normal boiling points, the standard molar entropy of vaporization is about 88 J>mol@K. (a) Estimate the normal boiling point of bromine, Br2, by determining ΔH°vap for Br2 using data from Appendix C. Assume that ΔH°vap remains constant with temperature and that Trouton's rule holds. (b) Look up the normal boiling point of Br2 in a chemistry handbook or at the WebElements website (www.webelements.com) and compare it to your calculation. What are the possible sources of error, or incorrect assumptions, in the calculation?

(b) Based on your general chemical knowledge, predict which of these reactions will have K 7 1. (i) 2 Mg1s2 + O21g2Δ2 MgO1s2 (ii) 2 KI1s2Δ2 K1g2 + I21g2 (iii) Na21g2Δ2 Na1g2 (iv) 2 V2O51s2Δ4 V1s2 + 5 O21g2

Trouton's rule says that the ratio of the molar heat of vapor-ization of a liquid to its normal boiling point (in kelvin) is approximately the same for all liquids: ∆Hvap/Tbp ≈ 88 J/(K*mol) (c) Which of the liquids in the table deviate(s) from Trouton's rule? Explain.

Trouton's rule says that the ratio of the molar heat of vapor-ization of a liquid to its normal boiling point (in kelvin) is approximately the same for all liquids: ∆Hvap/Tbp ≈ 88 J/(K*mol) (b) Explain why liquids tend to have the same value of ∆Hvap/Tbp.

Trouton's rule says that the ratio of the molar heat of vapor-ization of a liquid to its normal boiling point (in kelvin) is approximately the same for all liquids: ∆Hvap/Tbp ≈ 88 J/(K*mol) (a) Check the reliability of Trouton's rule for the liquids listed in the following table.

Chloroform has ΔHvaporization = 29.2 kJ>mol and boils at 61.2 °C. What is the value of ΔSvaporization for chloroform?