function dx = Model_obsv(t,x)

kBC=3;
kCB=2;
Vdot=1;
VR=10;
ca0 = 1;
dx = zeros(4,1);

dx(1) = Vdot/VR*(ca0 - x(1)) - x(4)*x(1);
dx(2) = -Vdot/VR * x(2) + x(4)*x(1) + kCB*x(3) - kBC*x(2)^2;
dx(3) = -Vdot/VR * x(3) - kCB*x(3) + kBC*x(2)^2;
dx(4) = 0;


