First order and second order reaction rates

[Cesar P]

How do we tell the difference between first order and second order ?

[Neil DSilva 1L]

When you're looking at a rate law, a first order reaction will have an overall order of one (the sum of all the exponents will be 1) and a second order reaction will have an overall order of 2 (the sum of all the exponents will be 2).

The exponents can be determined experimentally (for reactions with multiple reactants), by looking at the graphs of the natural log of the concentration vs. time (first order) or the reciprocal of the concentration vs. time (second order) and determining which one produces a straight line (for a single reactant reaction).

Another way to determine the order of the reaction is to look at the units of the k value (rate constant). For a first order reaction, k will have units of second^-1 and for a second order reaction, k will have units of L.mole^-1.second^-1.

[Chem_Mod]

Neil is correct.

[104607508]

how can we tell when a reaction will have a fractional rate order? is it when the products decompose into the reactants?