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144                               CHAPTER 5.  RATE OF GENERATION


             The mole fractions  of CzH4  and  CI&  are given in the problem statement.  These
             values  are used to deternine the extent of the reactions as
                                         E1
                               xc2n4 = - 0.25          j tl = 0.333
                                             =
                                       1 +e1
                                             -
                               XCH4 = - 0.05          +     ~2 = 0.033
                                        2E2
                                             -
                                       1 +E1
             Therefore, the mole fmctaons  of CzHs, H2  and  the inerts are
                                 0.85 - ~1 - €2 - 0.85 - 0.333 - 0.033 = 0,363
                                              -
                                    1+E1             1 + 0.333
                                          0.333 - 0.033
                                 --  -                = 0.225
                                 ~1 - ~2
                                 1+E1       1 f 0.333
                                   0.15   = 0.112
                                 1 + 0.333
             5.3.3  Rate of Reaction
             The rate of  a chemical reaction, r, is defined by


                                                                              (5.3-22)

             where V is the volume physically occupied by the reacting fluid.  Since both V and
             &/dt  are positive, the reaction rate is intrinsically positive. Note that the reaction
             rate has the units of  moles reacted per unit time per unit volume of  the reaction
             mixture. The reaction rate expression, T, has the following characteristics:

                0  It is an intensive property,
                0  It is independent of  the reactor type,
                0  It is independent of a process.

                Changes in the molar extent of  the reaction can be related to the changes in
             the number of  moles of  species i by differentiating Eq.  (5.3-10). The result is

                                                 1
                                            &= -dni                           (5.3-23)
                                                 ai
             Substitution of Eq.  (5.3-23) into Eq.  (5.3-22) gives

                                               1  1  dni
                                           r=---                              (5.3-24)

             If  the rate of  generation of  species i per unit volume, %i,  is defined by

                                                                              (5.3-25)
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