Question

Which of the following chemicals

Answer 1

For any reaction which is in equilibrium, such as:

\[A + B \rightarrow \leftarrow C + D\]
(you'll have to pretend there's an equilibrium sign above!)

the equilibrium constant (Keq) would be the ratio of the concentration of the products (C and D) to the reactants (A and B):
\[K _{eq} = \frac{ [C][D] }{ [A][B] }\]
So, the larger the numerator (i.e. the larger the concentrations of products over reactants at equilibrium), the larger the Keq value and the more the products are favoured over the reactants.

This depends on how stable the products are and their ability to revert back to form the original reactants in the opposite direction.

Answer 2

In each of the four equations (acid-base reactions), we have:

\[Acid + Base \rightarrow \leftarrow Conjugate~Base + Conjugate~Acid\]

Our acid loses/donates a proton to form the conjugate base and the base accepts this proton to form the conjugate acid. The weaker and more stable the conjugate acids and bases that are formed, the less likely they are to reform back to the original acid and base (i.e. the conjugate base gaining back its proton from the conjugate acid).

We also know that the stronger the acid, the weaker its conjugate base will be, and also the stronger the base, the weaker its conjugate acid. So to identify the reaction with the largest Keq, we need to find the one containing the strongest acids and bases in the reactants.

I'd say that the answer's either A or D, but I'm not 100% sure to be honest @taramgrant0543664

Answer 3

A weak acid dissociate very low, then the K will be small, a strong acid is practically totally dissociated then it K will be very big. You have to look for the strongest acid in the series.

Answer 4

Both B. and C. contain very weak acids in the form of H2O and CH3COOH respectively, so that's why I ruled them out of the running.

D. contains a much stronger acid (in HCl) than the H3PO4 in A., but the base in A. (NH4) I believe is stronger than the base in D (which is H2O). If I had to give an answer I would probably say it's D, but it's the bases that I'm a bit confused about myself.

Answer 5

It was D! :)

Answer 6

Great @vera_ewing !..... hopefully you understand a little bit about why this is the case. As @Cuanchi said, it must be down to the strength of the HCl (Strong Acid) over H3PO4 (Weak Base). The conjugate base in (D.) is Cl-, which is a chlorine atom with a full outer shell (octet) of 8 electrons. This means that it's very unreactive once formed and thus is very stable.

Although NH3 is a stronger base than H2O. both are relatively weak and so the musn't matter that much in comparing the Keq values!