Formula of an n-order model.

Given the reaction order $n$ , the function returns the equation corresponding to that particular n^th^-order kinetic model. For $n\neq 1$: $$y(t)=((n-1)\,k\,t+y_0^{1-n}))^{\frac{1}{n-1}}$$ for $n=1$: $$y(t)=y_0\,e^{-k\,t}$$