Finding Equilibrium Constant

[Chiara Frank]

Hey guys! How small must the equilibrium constant K be to assume the value for x is very small and that we can use the given molarity? Is it to the power of -3 or smaller, or -4 or smaller? There are a few questions on the Achieve homework and textbook problems in which we could do this, but I was not sure when. Thank you!

[Selene_Lam_1G]

I remember my TA mentioned that it should be 10^-4 or smaller!

[Nathan Tran 1B]

Yea Dr. Lavelle said to be safe do 10^-4 or smaller. But you should also check using the 5% rule after calculations to ensure that the assumption was correct.

[Kailin Mimaki 2K]

The equilibrium constant should be at least 10^-4 or smaller to ensure that we can cross out the x in our equation and approximate to find the value of x. In order to check that you can approximate, take the value of x, divide it by the initial amount, then multiply by 100. If it is less than 5%, you can approximate. Hope this helped!

[Aaron Kim 1J]

K should be at least 10^-4 or smaller. Though to check, after calculating the value of x, you can divide it by the initial concentration/partial pressure and multiply the quotient by 100. If the resulting percentage is less than 5%, you were correct to approximate.

[Nishan Reddy 3K]

I think that most people agree that anything smaller than 10^-4 is going to get rid of the x in the calculations. However, you should always check the value you calculate by dividing it by the initial concentration to make sure that it is less than 5% of the original. This makes it so that the simplification is justified.