Calculating the initial concentration without x

[Matt_Fontila_2L_Chem14B]

Today in lecture, Dr Lavelle covered ICE boxes in which we were able to calculate an initial concentration, given the final concentration, without using x in the change part of the ICE Box. How did he calculate the equilibrium molar concentration without x?

[Varsha Sivaganesh 1A]

It was because we were given the equilibrium concentration of the final product and the initial concentrations of the reactants. When doing an ice table, if you aren't given the initial concentration of the product, you assume it is 0. So for the problem that Dr. Lavelle did in class, the initial concentration of the product would be 0, and the equilibrium concentration was 0.150 M. So then for the change in concentration, you would just do .150M-0 = .150M. So that is the change and then for the reactants you would just make sure if there are stoichiometric coefficients in the equation to multiply by them. So in the equation N2 + 3H2 <--> 2NH3, the change in concentration for NH3 is 0.150M, so the change in concentration for N2 would be 0.150/2 = 0.75M.

Hope this helped!