Chem A level equilibrium questions (help please)

For the first one, it may help to write out your equilibrium equation, stating underneath the amount of starting A in terms of x and the left over in terns of x-y. You'll know the fraction of A left over is the (x-y)/x (left over/original amount).

You're next challenge will be to use Kc they've given to write a Kc equation in terms of the x and y and then work out what either x is in terms of y or the other way around. You'd sub this back into the first bit [(x-y)/y] and then you should be led to a clean answer.

The second one is pretty simple. Write your equilibrium reaction out. You should notice from the question that only ethanoic acid and ethanol was reacted so produces equal amounts of the products because they all have the same stoiceometric ratio and so the products will have equal concentrations. Knowing this, write a Kc equation equating it to your known value of Kc and then simplify it until you get to [CH3COOCH2CH3][H2O]=x. Because you know that the concentrations are the same, you've effectively got [H2O]^2=x or [CH3COOCH2CH3]^2=x. To work out the cincentrations, just square root the value of x.

Firstly thanks for the help. I get the explanation for the first one and an answer pops out fairly easily. But I still don't get your explanation for the second one. Could you please elaborate?

Hard to tell which part you missed.

The most important step is following the stoichiometry - please write the reaction equation and you will see that exactly the same amount of the ester and water are produced, so their concentrations must be identical. Everything else is just a simple algebra.

Basically what borek said. (Quoted below). Always write out your equation before you start any calculations.