Page 39 - The engineering of chemical reactions

Chemical Reactions 23

Figure 2-l The 12 reactions among 4
isomers of butylenes.

This is an extremely important reaction to which we will refer throughout this book. It is
responsible for all NO, formation in the atmosphere (the brown color of the air over large
cities) as well as nitric acid and acid rain. This reaction only occurs in high-temperature
combustion processes and in lightning bolts, and it occurs in automobile engines by free-
radical chain reaction steps, which will be the subject of Chapter 10. It is removed from
the automobile exhaust in the automotive catalytic converter, which will be considered in
Chapter 7.
The above reaction can also be written as
Nz+02+2NO
We could generalize these reactions as
fA+fB+C

or
A+B+2C
with A = Nz, B = 02, and C = NO. The coefficients of the chemical symbols in a reaction
are termed stoic&metric coefJicients, and it is evident that one can multiply all of them by
a constant and still preserve mass conservation.
We need to distinguish between stoichiometric coefficients of reactants and products.
For this we move all terms to the left with appropriate signs, so that the preceding reaction
becomes
-A-B+2C=O
Further, since the alphabet is limited, we will increase our capacity for naming chemicals
by naming a species j as Aj, so that this reaction is
-Al-A2+2A3=0
with Al = N2, AZ = 02, and A3 = NO. In this notation the generalized single reaction
becomes