Equilibrium Question

[tashlyc]

How can I tell if something is at equilibrium if I've been given the K value and the mols of the species? (I'm having trouble with question 6 c in the heinemann textbook in chapter 8.4)

[hahahaha]

Convert the mols to concentration then find a reaction quotient reaction with them. If it doesn't equal to the equilibrium constant for the reaction (which you've found in part b) then you'll know that it isn't at equilibrium.

[keltingmeith]

Slightly more worked through solution to hahahaha:

How can I tell if something is at equilibrium if I've been given the K value and the mols of the species? (I'm having trouble with question 6 c in the heinemann textbook in chapter 8.4)

Firstly, remember how to calculate K and Q:



The equations are exactly the same - the difference is when they are applied. If you calculate the expression at equilibrium, it's K. If you calculate it at any other time, it's Q. What follows, then, is the closer Q is to K, the closer you are to equilibrium. Furthermore, if you think you're calculating Q, and it turns out to be equal to K, then you must actually be equilibrium!

So, if you know what the K value SHOULD be, and you know the concentration of reactants and products at a particular time, you can calculate Q, and if Q=K, you're at equilibrium! Worked solution below in spoilers, so you can try the question out for yourself first:

Spoiler

Our equation is:


So, first we work out the concentrations by dividing each mol by 2, then evaluate Q.



Next, we need to see if this matches K. Next time, it would be appreciated if you could include your answer to previous parts of the question, in case they become necesarry like it is here. I've calculated K in this case to be 0.0198. Since Q is larger than K, there is more products than reactants, and so the current mixture will react more to form the reactants.

[tashlyc]

Thank you guys!! This helped a lot.