Thermodynamics

16–83 A constant-volume tank contains a mixture of 1 molof H 2 and 0.5 mol of O 2 at 25°C and 1 atm. The contents ofthe tank are ignited, and the final temperature and pressure inthe tank are 2800 K and 5 atm, respectively. If the combustiongases consist of H 2 O, H 2 , and O 2 , determine (a) the equilibriumcomposition of the product gases and (b) the amount ofheat transfer from the combustion chamber. Is it realistic toassume 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 216–84 A mixture of 2 mol of H 2 O and 3 mol of O 2 isheated to 3600 K at a pressure of 8 atm. Determine the equilibriumcomposition 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 isheated to 3400 K at a pressure of 2 atm. Determine the equilibriumcomposition of the mixture, assuming that only CO 2 ,CO, O 2 , and O are present. Answers: 1.313CO 2 , 1.687CO,3.187O 2 , 1.314O16–86 Reconsider Prob. 16–85. Using EES (or other)software, study the effect of pressure on theequilibrium composition by varying pressure from 1 atm to10 atm. Plot the amount of CO present at equilibrium as afunction of pressure.16–87 Estimate the enthalpy of reaction for the combustionprocess of hydrogen at 2400 K, using (a) enthalpydata and (b) K P data.Answers: (a) 252,377 kJ/kmol, (b) 252,047 kJ/kmol16–88 Reconsider Prob. 16–87. Using EES (or other)software, investigate the effect of temperatureon the enthalpy of reaction using both methods by varyingthe temperature from 2000 to 3000 K.16–89 Using the enthalpy of reaction data and the K Pvalue at 2800 K, estimate the K P value of the dissociationprocess O 2∆ 2O at 3000 K.16–90 Show that when the three phases of a pure substanceare in equilibrium, the specific Gibbs function of each phaseis the same.16–91 Show that when the two phases of a two-componentsystem are in equilibrium, the specific Gibbs function of eachphase of each component is the same.16–92 A constant-volume tank initially contains 1 kmol ofcarbon monoxide CO and 3 kmol of oxygen O 2 (no nitrogen)at 25°C and 2 atm. Now the mixture is ignited and the COburns completely to carbon dioxide CO 2 . If the final temperaturein the tank is 500 K, determine the final pressure in thetank and the amount of heat transfer. Is it realistic to assumethat there will be no CO in the tank when chemical equilibriumis reached?16–93 Using Henry’s law, show that the dissolved gases ina liquid can be driven off by heating the liquid.Chapter 16 | 82116–94 Consider a glass of water in a room at 25°C and 100kPa. If the relative humidity in the room is 70 percent and thewater 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 tothe water surface, and (c) the mole fraction of air in the waternear the surface.16–95 Repeat Prob. 16–94 for a relative humidity of25 percent.16–96 A carbonated drink is fully charged with CO 2 gas at17°C and 600 kPa such that the entire bulk of the drink is inthermodynamic equilibrium with the CO 2 –water vapor mixture.Now consider a 2-L soda bottle. If the CO 2 gas in thatbottle were to be released and stored in a container at 20°Cand 100 kPa, determine the volume of the container.16–97 Ethyl alcohol (C 2 H 5 OH(g)) at 25°C is burnedin a steady-flow adiabatic combustion chamberwith 40 percent excess air that also enters at 25°C. Determinethe adiabatic flame temperature of the products at 1 atmassuming the only significant equilibrium reaction is CO 2 1CO 2 O 2 . Plot the adiabatic flame temperature as the percentexcess air varies from 10 to 100 percent.16–98 Tabulate the natural log of the equilibrium constantas a function of temperature between 298h Rto 3000 K for the equilibrium reaction CO H 2 O CO 2 H 2 . Compare your results to those obtained by combining theln K P values for the two equilibrium reactions CO 2 CO 112 O 2 and H 2 O H 2 2 O 2 given in Table A–28.16–99 It is desired to control the amount of CO in theproducts of combustion of octane C 8 H 18 so thatthe volume fraction of CO in the products is less than 0.1hpercent. Determine the percent theoretical air required for theRcombustion of octane at 5 atm such that the reactant andproduct temperatures are 298 K and 2000 K, respectively.Determine the heat transfer per kmol of octane for thisprocess if the combustion occurs in a steady-flow combustionchamber. Plot the percent theoretical air required for 0.1 percentCO in the products as a function of product pressuresbetween 100 and 2300 kPa.Fundamentals of Engineering (FE) Exam Problems16–100 If the equilibrium constant for the reaction H 2 12 O 2 S H 2 O is K, the equilibrium constant for the reaction2H 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 216–101 If the equilibrium constant for the reaction CO 12 O 2 S CO 2 is K, the equilibrium constant for the reactionCO 2 3N 2 S CO 1 2 O 2 3N 2 at the same temperature is(a) 1/K (b) 1/(K 3) (c) 4K (d) K (e) 1/K 2