Let's follow the same procedure that was used in Example 9.4, even though the reactor is isothermal.

gasConst = 1.987;
deltaHrxn = -8000;
equilConst300 = 10;
equilConst400 = 
      equilConst300*
        Exp[-deltaHrxn/gasConst*(1/400 - 1/300)]

equilConst = 
        equilConst300*
          Exp[-deltaHrxn/
                gasConst*(1/temp - 1/300)];
xAe = equilConst/(equilConst + 1);
Plot[xAe, {temp, 260, 440}, GridLines -> Automatic, 
        AxesOrigin -> {260, 0}];

k1 = 10^3*Exp[-2416/temp]
k2 = k1/equilConst

cA0 = 1.0;   
rate4 = 0.005;
rate5 = 0.01;
rate6 = 0.015;
rate7 = 0.02;
rate8 = 0.03;
rate9 = 0.04;
rate10 = 0.05;
rate11 = 0.07;
rate12 = 0.1;
rate13 = 0.15;
rate14 = 0.2;
rate15 = 0.3;
rate16 = 0.4;
rate17 = 0.5;
rate18 = 0.6;
rate19 = 0.7;
rate20 = 0.8;
rate21 = 0.9;
rate22 = 1.0;
rate23 = 1.2;
rate24 = 1.4;
rate25 = 1.6;
rate26 = 1.8;
rate27 = 2.0;
rate28 = 2.5;
rate29 = 3.0;
rate30 = 4.0;
rate31 = 5.0;
xA4 = (k1*cA0 - rate4)/(k1*cA0 + 
              k2*cA0);
xA5 = (k1*cA0 - rate5)/(k1*cA0 + 
              k2*cA0);
xA6 = (k1*cA0 - rate6)/(k1*cA0 + 
              k2*cA0);
xA7 = (k1*cA0 - rate7)/(k1*cA0 + 
              k2*cA0);
xA8 = (k1*cA0 - rate8)/(k1*cA0 + 
              k2*cA0);
xA9 = (k1*cA0 - rate9)/(k1*cA0 + 
              k2*cA0);
xA10 = (k1*cA0 - rate10)/(k1*cA0 + 
              k2*cA0);
xA11 = (k1*cA0 - rate11)/(k1*cA0 + 
              k2*cA0);
xA12 = (k1*cA0 - rate12)/(k1*cA0 + 
              k2*cA0);
xA13 = (k1*cA0 - rate13)/(k1*cA0 + 
              k2*cA0);
xA14 = (k1*cA0 - rate14)/(k1*cA0 + 
              k2*cA0);
xA15 = (k1*cA0 - rate15)/(k1*cA0 + 
              k2*cA0);
xA16 = (k1*cA0 - rate16)/(k1*cA0 + 
              k2*cA0);
xA17 = (k1*cA0 - rate17)/(k1*cA0 + 
              k2*cA0);
xA18 = (k1*cA0 - rate18)/(k1*cA0 + 
              k2*cA0);
xA19 = (k1*cA0 - rate19)/(k1*cA0 + 
              k2*cA0);
xA20 = (k1*cA0 - rate20)/(k1*cA0 + 
              k2*cA0);
xA21 = (k1*cA0 - rate21)/(k1*cA0 + 
              k2*cA0);
xA22 = (k1*cA0 - rate22)/(k1*cA0 + 
              k2*cA0);
xA23 = (k1*cA0 - rate23)/(k1*cA0 + 
              k2*cA0);
xA24 = (k1*cA0 - rate24)/(k1*cA0 + 
              k2*cA0);
xA25 = (k1*cA0 - rate25)/(k1*cA0 + 
              k2*cA0);
xA26 = (k1*cA0 - rate26)/(k1*cA0 + 
              k2*cA0);
xA27 = (k1*cA0 - rate27)/(k1*cA0 + 
              k2*cA0);
xA28 = (k1*cA0 - rate28)/(k1*cA0 + 
              k2*cA0);
xA29 = (k1*cA0 - rate29)/(k1*cA0 + 
              k2*cA0);
xA30 = (k1*cA0 - rate30)/(k1*cA0 + 
              k2*cA0);
xA31 = (k1*cA0 - rate31)/(k1*cA0 + 
              k2*cA0);
Plot[{xA4, xA5, xA6, xA7, xA8, xA9, xA10, xA11, xA12, xA13, xA14, 
          xA15, xA16, xA17, xA18, xA19, xA20, xA21, xA22, xA23, xA24, xA25, 
          xA26, xA27, xA28, xA29, xA30, xA31, xAe}, {temp, 290, 410}, 
        PlotRange -> {0. , 1. }, AxesOrigin -> {290, 0}, 
        GridLines -> {{290, 295, 300, 305, 310, 315, 320, 325, 330, 335, 
              340, 345, 350, 355, 360, 365, 370, 375, 380, 385, 390, 395, 
              400, 405, 410}, {0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 
              0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 
              1.0}}];

The above graph can be used to solve Problem 9.12 (see Example 9.5). Make sure it's correct! But, do you REALLY need it? Solve the same problem "the old fashioned way" (see Chapter 5).