I've found sth myself! Is it C0*K?? C0(initial concentration (mg.L-1)) and K(min-1).

To see that the reaction (A -> products) is of the first order, perform a batch experiment for several initial concentrations of substrate A. If it turns out that the points (cAo-cA (t))/cAo lie on one curve, it is proof that the reaction is of the first order. Only then the plot ln(cA/cAo) vs time make sense. If the kinetic data can be described by the kinetic equation of L-H type, for example rA = acA / (1 + bcA), then such a reaction has no order.

If ro=a then the unit is 1/s. You can also use a dimensionless variable (eg cA/cAo), then the unit of ro is kg m-3 s-1 (SI). Regards,

Hello,

you can load this paper to find a suitable answer.

Best regards,

The publication recommended above (vip ?) is an example of direct transfer of well-established knowledge in the field of engineering of chemical reactions to other areas of knowledge. Regardless of whether the chemical reaction takes place in the presence of a catalyst or not, whether it is additionally stimulated by UV light the basic principles of kinetic research and related concepts and terms remain unchanged. Thus, the reaction: A (eg dye) -> degradation products is of the first order if its rate is proportional to the concentration of substrate A (omitting rather unlikely inhibitory or enhancing effect of products). Consequently, the kinetic equation of the chemical reaction has the form r = kcA and what is the most important the conversion degree of reaction does not depend on the initial substrate concentration and the volume of the reaction mixture. Such information can be found in any book on chemical reaction engineering.

The work involved kinetic studies of photocatalytic MY degradation. The effect of initial catalyst concentration and initial dye concentration was investigated. One can of course use the power function to approximate the dependence between kobs and catalyst concentration, although it is much better to use the exponential (y=a(1-exp(-bx)) or hyperbolic (y=ax/(1+bx)) function here. Why - I hope I do not have to explain. I have also doubts to the description of kinetic curves C = f(t) obtained for different Co values. If it turns out that the experimental points (Co-C(t))/Co lie on one curve, then using the kinetic equation r = kC would be justified. However, it is not (kobs = var). Of course, as it was done in "vip", to describe such data, one can use the equation in the form r = kobsC = kcKLHC/(1 + KLHCo) and then use it in the mass balance -dC/dt = r. However, the use in such situation the term "L-H rate expresion" or "L-H kinetic model" and interpreting the parameters of this in fact empirical equation I consider unjustified. It is also unjustified to use the term "pseudo first-order kinetics". I would also have doubts to treat the product kcKLH as a reaction rate constant (r = kcKLHC/(1 + KLHCo) is not kinetic equation).

You can of course use such an empirical approach. However, I say once more, assigning a physical meaning to the individual parameters of the above equation will be debatable. Instead, you can use kinetic equations in the form r = kCn (n – reaction order) or r = kC/(1 + KC) (L-H, M-M, Monod, hyperbolic etc. model). It is up to you. Regards,

Thank you Dr.Grzesik and Dr. Ahmed. That was really useful.

Sincerely yours.