Calculating Equilibrium Composition

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Vanessa Romero-Campos 2B
Posts: 39
Joined: Fri Sep 25, 2015 3:00 am

Calculating Equilibrium Composition

Postby Vanessa Romero-Campos 2B » Mon Nov 09, 2015 12:00 am

An example in the course reader asks to find K.
It states: Mix .500 mol*L-1 N2 with .800 mol*L-1 H2. Also given at equilibrium there's .150 mol*L-1 NH3. What's K.

The balanced equation is 1 mole N2 + 3 mole H2 <--> 2 mole NH3
The chart looks like this:
N2 H2 NH3
Initial Molar concentration .500 .800 0
change in Molar concentration -.075 -.225 .150
equilibrium Molar concentration .425 .575 .150

To find K I have to use the formula k= products/reactants
Kc= [NH3]2/[N2][H2]3
= (.150)2/(.425)(.575)3

My question is: Where do the exponents come from? That totally lost me.

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Re: Calculating Equilibrium Composition

Postby Chem_Mod » Mon Nov 09, 2015 12:29 am

The exponents are from the moles in the balanced equation. For each reactant or product, you raise the concentration or partial pressure to the power of the stoichiometric coefficient.

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