Chapter 16 | 82116–83 A constant-volume tank contains a mixture of 1 mol
of H 2 and 0.5 mol of O 2 at 25°C and 1 atm. The contents of
the tank are ignited, and the final temperature and pressure in
the tank are 2800 K and 5 atm, respectively. If the combustion
gases consist of H 2 O, H 2 , and O 2 , determine (a) the equilib-
rium composition of the product gases and (b) the amount of
heat transfer from the combustion chamber. Is it realistic to
assume that no OH will be present in the equilibrium mixture?
Answers:(a) 0.944H 2 O, 0.056H 2 , 0.028O 2 , (b) 132,574 J/mol H 2
16–84 A mixture of 2 mol of H 2 O and 3 mol of O 2 is
heated to 3600 K at a pressure of 8 atm. Determine the equi-
librium composition of the mixture, assuming that only H 2 O,
OH, O 2 , and H 2 are present.
16–85 A mixture of 3 mol of CO 2 and 3 mol of O 2 is
heated to 3400 K at a pressure of 2 atm. Determine the equi-
librium composition of the mixture, assuming that only CO 2 ,
CO, O 2 , and O are present. Answers:1.313CO 2 , 1.687CO,
3.187O 2 , 1.314O
16–86 Reconsider Prob. 16–85. Using EES (or other)
software, study the effect of pressure on the
equilibrium composition by varying pressure from 1 atm to
10 atm. Plot the amount of CO present at equilibrium as a
function of pressure.
16–87 Estimate the enthalpy of reaction for the com-
bustion process of hydrogen at 2400 K, using (a) enthalpy
data and (b) KPdata.
Answers:(a) 252,377 kJ/kmol, (b)252,047 kJ/kmol
16–88 Reconsider Prob. 16–87. Using EES (or other)
software, investigate the effect of temperature
on the enthalpy of reaction using both methods by varying
the temperature from 2000 to 3000 K.
16–89 Using the enthalpy of reaction data and the KP
value at 2800 K, estimate the KPvalue of the dissociation
process O 2 2O at 3000 K.
16–90 Show that when the three phases of a pure substance
are in equilibrium, the specific Gibbs function of each phase
is the same.
16–91 Show that when the two phases of a two-component
system are in equilibrium, the specific Gibbs function of each
phase of each component is the same.
16–92 A constant-volume tank initially contains 1 kmol of
carbon monoxide CO and 3 kmol of oxygen O 2 (no nitrogen)
at 25°C and 2 atm. Now the mixture is ignited and the CO
burns completely to carbon dioxide CO 2. If the final tempera-
ture in the tank is 500 K, determine the final pressure in the
tank and the amount of heat transfer. Is it realistic to assume
that there will be no CO in the tank when chemical equilib-
rium is reached?
16–93 Using Henry’s law, show that the dissolved gases in
a liquid can be driven off by heating the liquid.∆hRhR16–94 Consider a glass of water in a room at 25°C and 100
kPa. If the relative humidity in the room is 70 percent and the
water and the air are in thermal equilibrium, determine
(a) the mole fraction of the water vapor in the room air,
(b) the mole fraction of the water vapor in the air adjacent to
the water surface, and (c) the mole fraction of air in the water
near the surface.
16–95 Repeat Prob. 16–94 for a relative humidity of
25 percent.
16–96 A carbonated drink is fully charged with CO 2 gas at
17°C and 600 kPa such that the entire bulk of the drink is in
thermodynamic equilibrium with the CO 2 –water vapor mix-
ture. Now consider a 2-L soda bottle. If the CO 2 gas in that
bottle were to be released and stored in a container at 20°C
and 100 kPa, determine the volume of the container.
16–97 Ethyl alcohol (C 2 H 5 OH(g)) at 25°C is burned
in a steady-flow adiabatic combustion chamber
with 40 percent excess air that also enters at 25°C. Determine
the adiabatic flame temperature of the products at 1 atm
assuming the only significant equilibrium reaction is CO 2
CO O 2. Plot the adiabatic flame temperature as the per-
cent excess air varies from 10 to 100 percent.
16–98 Tabulate the natural log of the equilibrium con-
stant as a function of temperature between 298
to 3000 K for the equilibrium reaction CO H 2 O CO 2
H 2. Compare your results to those obtained by combining the
ln KPvalues for the two equilibrium reactions CO 2 CO
O 2 and H 2 O H 2 O 2 given in Table A–28.
16–99 It is desired to control the amount of CO in the
products of combustion of octane C 8 H 18 so that
the volume fraction of CO in the products is less than 0.1
percent. Determine the percent theoretical air required for the
combustion of octane at 5 atm such that the reactant and
product temperatures are 298 K and 2000 K, respectively.
Determine the heat transfer per kmol of octane for this
process if the combustion occurs in a steady-flow combustion
chamber. Plot the percent theoretical air required for 0.1 per-
cent CO in the products as a function of product pressures
between 100 and 2300 kPa.Fundamentals of Engineering (FE) Exam Problems
16–100 If the equilibrium constant for the reaction H 2
is K, the equilibrium constant for the reaction
2H 2 O →2H 2 O 2 at the same temperature is
(a) 1/K (b) 1/(2K)(c) 2K (d) K^2 (e) 1/K^2
16–101 If the equilibrium constant for the reaction CO
is K, the equilibrium constant for the reaction
at the same temperature is
(a) 1/K (b) 1/(K3) (c) 4K (d) K (e) 1/K^2CO 2 3N 2 SCO^12 O 2 3N 21
2 O^2 SCO^21
2 O 2 SH 2 O1
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