Environmental Engineering Reference
In-Depth Information
p
i
reaction order with respect to species i
[
-
]
mol
−1
K
−1
]
R
u
universal gas constant
[=8.314 J
m
−3
s
−1
]
r
reaction rate
[mol
mol
−1
K
−1
]
S
entropy
[J
T
temperature
[K]
t
time
[s]
[m
3
]
V
volume
x
i
number of moles of species i reacted
[mol]
y
i
mole fraction of species i
[
-
]
mol
−1
]
Δ
r
H reaction enthalpy
[J
mol
−1
]
λ
j
Lagrangian multiplier
[J
mol
−1
]
μ
i
chemical potential of component i
[J
ν
stoichiometric coefficient
[
-
]
Subscripts
b
backward direction
env
related to the environment surrounding a system
f
forward direction
syst
system
tot
total
Superscripts
t
total
5.1 REACTION KINETICS
Combustion is an example of a chemical reaction and can thus be described by a
reaction equation. For example, the combustion of methane can be written as
CH
4
+2O
2
!
CO
2
+2H
2
O
ð
RX
:
5
:
1
Þ
This
overall reaction equation
states that if a reaction takes place, this will advance
according to the molar and mass balances of the reaction itself, but it says nothing
about the real reactionmechanism(usually formed bymany elementary reactions). From
(RX. 5.1),weknowthat 1mol ofmethane reactswith2mol ofmolecular oxygen togive 1
mol of carbon dioxide and 2 mol of water. Considering that in chemistry, species mass is
computed by multiplying the atomic weight (in atomic mass units) of each element in a
chemical formula by the number of atoms of that element present in the formula, then
adding all of these products together gives 16 (12 + 4) g of methane and 64 (2 × 32) g
of molecular oxygen form 44 (12 + 32) g of carbon dioxide and 36 (2 × 18) g of water.
Search WWH ::
Custom Search