{ diff(x1, t) = ((-1)*x1*k8*k3*k2 + (-1)*x1*x4*k4*k2 + 1*x3*k7*k2)/k2,
  diff(x2, t) = 0,
  diff(x3, t) = (1*k8*x4*k5*k2 + (-1)*x3*k7*k2)/k2,
  diff(x4, t) = (1*x1*k8*k3*k2 + (-1)*x1*x4*k4*k2 + 1*k8*x4*k5*k2 + (-2)*x4^2*k6*k2)/k2,
  diff(x5, t) = 0 }