Extension of the second order rate concept

In Biosciences one of the most common applications of a second order kinetics is the interaction of a ligand with its receptor, thus forming a receptor/ligand complex 

We can write a general rate equation for this type of reaction (since we look at the disappearance of the reactants the rate is negative)  

Each receptor binds 1 ligand and therefore the ratio is 1 1 (which makes life a lot easier for us). For each mole of R used one mole of L must be used as well. 

Second order reaction with different reactants 

We assume the rate equation is a first order reaction with respect to R, and also a first order reaction with respect to L. However, since there are the concentrations of two components involved, the overall order of the reaction is second order. 

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