## Powers of Concentrations in Rate Law

$aR \to bP, Rate = -\frac{1}{a} \frac{d[R]}{dt} = \frac{1}{b}\frac{d[P]}{dt}$

Merzia Subhan 1L
Posts: 33
Joined: Thu Jul 13, 2017 3:00 am

### Powers of Concentrations in Rate Law

Since when writing rate laws, the coefficients of the equation are not the power in the rate law, like 3 I- is not [I-]^3, how would you determine the power of a concentration in a rate law? Is it impossible to determine just by looking at the chemical equation?

DianaTrujillo2K
Posts: 40
Joined: Fri Sep 29, 2017 7:04 am

### Re: Powers of Concentrations in Rate Law

The order of a rate law is determined experimentally using the method of initial rates or by looking at the graphs. When the observed rate law is given along with the elementary steps of a reaction, you can use the pre-equilibrium approach to determine the slow step that determines the rate of the overall reaction. In the pre-equilibrium approach the coefficients of the reactants are the powers of their concentrations.

Angel R Morales Dis1G
Posts: 50
Joined: Sat Jul 22, 2017 3:01 am

### Re: Powers of Concentrations in Rate Law

You can write the rate law from the the formula itself, A+B -> C, r=k[A][B], but you wouldnt know what order it is until you find the exponents to each reactant, most likely from a data table.