Question 11.13

[Annah Khan 1B]

"Write the reaction quotient Q for:
(a) 2 BCl3(g) + 2 Hg (l) --> B2Cl4 (s) + Hg2Cl2 (s)
(b) P4S10 (s) + 16 H2O (l) --> 4 H3PO4 (aq) + 10 H2S (aq)
(c) Br2 (g) + 3 F2 (g) --> 2 BrF3 (g)"

As I understand, Q is equal to [products]/[reactants]. However, the answer for (a) is 1/PBCl3^2, and I am not sure how to get that answer. I feel like I'm overthinking this one, but if anyone could help me out, that would be great. Thanks!

[Johana Jeon 1A]

The reason why the answer is 1/PBCl3^2 is because as stated in page 133 in the course reader, molar concentration of a pure substance (solid or liquid) does not change in a reaction
This means that solid + liquid are not included in K expression

As you can see in problem A, 2 BCl3(g) + 2 Hg (l) --> B2Cl4 (s) + Hg2Cl2 (s)
2 BCl3 is gas
2 Hg is liquid
B2Cl4 is solid
And Hg2Cl2 is solid



We know that Q = [products] / [reactants]
Therefore, the only thing left in the [product] is 1 and [reactant] is PBCl3^2
Hope that made sense!!

[604744616]

So just to review this both solids, liquids and aqueous are not included in the concentrations?

[Johana Jeon 1A]

Aqueous is included
Only solid + liquid NOT included