Modern Engineering Thermodynamics

644 CHAPTER 15: Chemical Thermodynamics
and
ðT A Þ closed
system = T°+
h f
° fuel −∑ R
ðn i /n fuel
where ðc pi Þ avg and ðc vi Þ avg are found in Tables 15.5 and 15.6.
10. Molar specific entropy production for a chemical reaction:
ðs P
Þ r
= ∑
P
ðn i /n fuel
∑
P
Þs i −∑
R
ÞRT° −∑
R
ðn i /n fuel
11. Absolute molar specific entropy at temperature T and pressure p:
and
12. Molar specific entropy of formation:
sp,T ð Þabs
incompressible
substance
½sðp,TÞ abs
Š ideal
gas
13. Molar specific Gibbs function of formation:
ðs f °Þ compound
= s° compound −
= s°+c p ln ðT/T°
ðn i /n fuel Þðh f
° − RT°Þ i
Þðc vi Þ avg
ðn i /n fuel Þs i − q r /T b
= s°+c ln ðT/T°
Þ
∑
elements
Þ− R ln ðp/p°
Þ
n i /n compound
si °
ðg f °Þ compound = ðh f
°Þ compound − T°ðs f °Þ compound
14. Molar specific Gibbs function at the reference state of 0.1 MPa and the products or reactants mixture
temperature T:
g • i ðat p°, TÞ = ðg f °Þ i + ½ðhðat TÞ − ðh °ðat T°ÞŠ i − T½sðat p°, TÞŠ i + T°½s°ðat p°, T°ÞŠ i
15. Chemical equilibrium constant, based on Gibbs functions:
2
∑
R
K e = exp6
’
4
and, based on molar concentrations:
16. The van’t Hoff equation:
17. Fuel cell maximum reaction efficiency:
ðη r Þ maximum
fuel cell
efficiency
=
∑
R
18. Fuel cell open circuit voltage:
ðn i /n fuel
ϕ o =
K e =
Þg • i −∑
P
∏
P ′
∏
R ′
ð Þ v i
χ i
v i g • i −∑ v i g • i
P ’
RT
ðχ i Þ vi
∑
p m P ′
p°
dð ln K e Þ
dT
= _ Q r
RT 2
3
7
5
!
v i −∑ v i
R ′
ðn i /n fuel Þg • i + RT ln ∏ ðp i /p°
∑
R
ðn i /n fuel
Þh i −∑
P
R
ðn i /n fuel Þh i
ð
Þ ni/n fuel Þ /∏
P
" #
ðη r Þ max
∑ ðn i /n fuel Þh i −∑ ðn i /n fuel Þh i
fuel cell R
P
jF
ðp i /p°
ð
Þ ni/n fuelÞ