Chemical Reactions

Q
(i = Reactants, and
Q
cv
cv
where
2
_
+ ΣN
h = W
i
_
_
= ΣN
h − ΣN
h
_
o
f
Remark : h
e
i
e
_
o
f
cv
+ ΣN
i
_
e = Products, W
_
_
o
h = h + ( h−
h ),
_
o
f
_
o
f
( g)
= h
_
i
298K
_
( l)
+ h
e
_
h
e
_
o
( h
cv
= 0)
_
= h
Assume air and combustion gases are ideal gases, get data from the property tables
h
h
Substitute, Q cv
= 363,880 kJ/kmol fuel 8,270 kJ/kg fuel Q dot
= m dot
Q = 6.89 kW
_
280K
_
298K
1500K
Substance (kJ/kmol) (kJ/kmol) (kJ/kmol) (kJ/kmol)
C3H8(
l)
-118,910 0 NA NA
O2
0 8,682 8,150 49,292
N2
0 8,669 8,141 47,073
H 2O(
g)
- 241,820 9,904 NA 57,999
CO -393,520 9,364 NA 71,078
CO -110,530 8,669 NA 47,517
fg
h
h
)
Example 15.7 First Law Analysis of Combustion in a Bomb
Constant volume tank contains 1 kmol of methane (CH 4 ) gas
and 3 kmol of O 2 at 25 o C and 1 atm. The contents of the
tank are ignited, and the methane gas burns completely. If
the final temperature is 1,000K, determine (a) the final
pressure in the tank and (b) the heat transfer during this
process.
Solution: Concepts
1. Write chemical reaction equation
Assume ideal gas for both reactants and
products: PV = NR u T P 2
2. Energy balance: SSSF
Q = U P –U R
= (H p -P P V) - (H R -P R V)
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