function dfdV=prob624fun(V,x)
fa=x(1);
fb=x(2);
fc=x(3);
fd=x(4);
fe=x(5);
ff=x(6);
ft=fa+fb+fc+fd+fe+ff;
T=315.8;
P0=160;
k1=0.933*exp((2.5*(31400/1.987*(1/330-1/T))));
K1=131667*(0.00198*T)^2*exp(30620/1.987*(1/T-1/298));
k2=0.636*exp(18000/1.987*(1/300-1/T));
K2=103943*exp(9834/1.987*(1/T-1/298));
k3=0.244*exp(1.5*28956/1.987*(1/325-1/T));
ct0=P0/(0.082*T);
ca=ct0*(fa/ft);
cb=ct0*fb/ft;
cc=ct0*fc/ft;
cd=ct0*fd/ft;
ce=ct0*fe/ft;
cf=ct0*ff/ft;
r3c=-k3*cc;
r1a=-k1*(ca*cb^2-cc/K1);
r2a=-k2*(ca*cd-ce*cb/K2);
dfadV=r1a+r2a;
dfbdV=2*r1a-r2a-r3c;
dfcdV=-r1a+r3c;
dfddV=r2a;
dfedV=-r2a;
dffdV=-r3c;
dfdV = [dfadV;dfbdV;dfcdV;dfddV;dfedV;dffdV];

