[Aedan]

Hello,

i have a problem understanding the calculation of the reaction rate.

We have A + B  C + D. Let's assume we have a irreversible Reaction that is of certain orders ni with respect to the reacting components.
So my reaction rate is dependant of concentrations ci: r = k * cA^nA * cB^nB in [mol/(kg m3)]

The reaction rate constant has different units for different reactions right? Otherwise you wouldn't get [mol/(kg m3)].

Also where do you get equations for specific reactions? Are there databases (free) where you can fight such information? In the literature i found there are examples without specific numbers and they say it doesn't make sense to model a chemical reaction right from the start but rather get the necessary data for an empirical reaction rate equation from experiments.

[Corribus]

Rate laws are empirical in nature. There is no general way to determine them from first principles based just on the reaction equation, because often the mechanism of the reaction isn't readily apparent.   

[Aedan]

Yes...unfortunately . Are there any free sources avaiable to students that include empirical data/equations for important chemical reactions?

[Corribus]

Empirical data is hard to generalize, because it depends on starting conditions. I'm not sure off the top of my head if there are rate databases out there or not. I suspect not, but I could be wrong.