Page 303 - Advanced Thermodynamics for Engineers, Second Edition

292 CHAPTER 12 CHEMICAL EQUILIBRIUM AND DISSOCIATION

P12.8. A mixture of propane and air with an equivalence ratio 0.9 (i.e. a weak mixture) is
3
contained in a rigid vessel with a volume of 0.5 m at a pressure of 1 bar and 300 K. It is
ignited and after combustion the products are at a temperature of 2600 K and a pressure of
9.06 bar. Calculate
(a) the amount of substance in the reactants;
(b) the amount of substance in the products and
(c) the amount of substance in the products per unit amount of substance supplied in the fuel.
[0.02005; 0.02096; 0.0932; 0.1368; 0.01138; 0.00261; 0.02792; 0.7281]
P12.9. A stoichiometric mixture of carbon monoxide and air reacts in a combustion chamber,
forms exhaust products at 3000 K and 1 bar. If the products are in chemical equilibrium, but
no reactions occur between the nitrogen and the oxygen, show that the molar fraction of
carbon monoxide is approximately 0.169. The products of combustion now enter a heat
exchanger where the temperature is reduced to 1000 K. Calculate the heat transfer from the
products per amount of substance of CO 2 in the gases leaving the heat exchanger if
dissociation can be neglected at the lower temperature.
[ 399.3 MJ/kmol CO 2 ]
P12.10. A mixture containing hydrogen and oxygen in the ratio of 2:1 by volume is contained in a
rigid vessel. This is ignited at 60 C and a pressure of 1 atm (1.013 bar), and after some

time the temperature is 2227 C. Calculate the pressure and the molar composition of the

mixture.
[5.13 bar; 96.5%; 2.36%; 1.18%]
P12.11. A vessel is filled with hydrogen and carbon dioxide in equal parts by volume and the
mixture is ignited. If the initial pressure and temperature are 2 bar and 60 C respectively

and the maximum pressure is 11.8 bar, estimate
(a) the maximum temperature;
(b) the equilibrium constant, K p and
(c) the volumetric analysis of the products at the maximum temperature.
Use
1354
;
10
T
log K p ¼ 1:3573
p H 2 O p CO
;
p
where K p ¼
p H 2 CO 2
and T ¼ temperature in kelvin:
[1965; 4.6573; 0.3417; 0.3417; 0.1583; 0.1583]
P12.12. A stoichiometric mixture of hydrogen and air is compressed to 18.63 bar and 845 C. It burns

adiabatically at constant volume. Show that the final equilibrium temperature is 3300 K and
the degree of dissociation is 8.85%. Calculate the final pressure after combustion. Show the
process, including the effect of dissociation, on a U–T diagram. The equilibrium constant is

¼ 12:1389
ðp H 2 O =p 0 Þ
Kp r ¼
1=2
ðp H 2 =p 0 Þðp O 2 =p 0 Þ
at T ¼ 3300 K: