## Equilibrium Composition

donnanguyen1d
Posts: 64
Joined: Fri Sep 29, 2017 7:04 am

### Equilibrium Composition

When calculating Equlibrium Composition when do we know to approximate or use the quadratic equation? And in approximation, what are we approximating?

Curtis Tam 1J
Posts: 105
Joined: Thu Jul 13, 2017 3:00 am

### Re: Equilibrium Composition

I believe you approximate when you know the Kc value is really small, meaning any change "x" would be negligible, though it wouldn't be equal to zero. Is this what you are talking about?

Posts: 23
Joined: Fri Sep 29, 2017 7:05 am
Been upvoted: 1 time

### Re: Equilibrium Composition

When the values of change in molar concentration and equilibrium in molar concentration are unknown (x), the answer you will get will be in terms of x. Thus, since this variable is unknown, we set it equal to 0 and use the quadratic equation to solve for x. If you have enough information from the problem, this won't be necessary if you aren't using variables in your problem solving.

Cassandra Mullen 1E
Posts: 54
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 2 times

### Re: Equilibrium Composition

When you make x negligible under the small x assumption, you should check to make sure that you can use this assumption. To do this, calculate that the x value you get is less than 5% of the original concentration.

AnuPanneerselvam1H
Posts: 52
Joined: Fri Sep 29, 2017 7:07 am

### Re: Equilibrium Composition

When calculating the concentrations of products/reactants, we can approximate if the equilibrium constant is very small (<10^-5). This does not x is zero, but that x is very small and has a negligible effect.