## Pre-equilibrium approach

$K = \frac{k_{forward}}{k_{reverse}}$

Lauryn Shinno 2H
Posts: 59
Joined: Fri Sep 28, 2018 12:24 am

### Pre-equilibrium approach

When do you leave the equilibrium constants and when do you substitute k/k'? For example, in the one Dr. Lavelle did in lecture, he got rate=2k2*K*[NO]^2*[O2]. He then replaced K with k1/k1' to get rate=2k2*k1/k1'*[NO]^2*[O2]. Do you always replace K or are there times where you have to leave it in?

Jessica Castro 2H
Posts: 60
Joined: Fri Sep 28, 2018 12:29 am

### Re: Pre-equilibrium approach

Since K is unitless, it is better to try to replace K with k/k' when possible to be consistent with units. It is also easier to understand the concentrations of the reactants when k is used instead of K.

Emily Huang 1E
Posts: 30
Joined: Fri Sep 28, 2018 12:20 am

### Re: Pre-equilibrium approach

replacing K helps with understanding the rate of the reactions. When writing the rate law, you use rate constants and not K as K just means the reaction is at equilibrium, Having k/k' is more representative of rates in relation to concentration