function dx=p426sbfun(t,x)
Vi=200;
v0=0.05;
ca0=7.72;
cb0=10.93;
na0=ca0*Vi;
fb0=0.05*cb0;
k=9e-5;
kc=1.08;
na=x(1);
nb=x(2);;
nc=x(3);
nd=x(4);
V=Vi+v0*t;
ca=na/V;
cb=nb/V;
cc=nc/V;
cd=nd/V;
r=k*(ca*cb-(cc*cd)/kc);
ra=-r*V;
rb=fb0-r*V;
rc=r*V;
rd=r*V;
dx = [ra;rb;rc;rd];

