Question

Which of the following is the correct expression for the rate of the following reaction? Note: not all species are gaseous.

CuO(s) + H2S (g) <--> Cu(s) + H2O (g)


a) [H2O] / [H2S]

b) None of these are correct

c) [Cu] x [H2O] / ([CuO] x [H2S])

d) [CuO] x [H2S] / ([Cu] x [H2O])

Answer 1

Equilibrium constants are written to include only aqueous and gaseous species. Solids and pure liquids are considered to have activities of 1, and are omitted. So, for the reaction

CuO(s)+H2S(g)⇌CuS(s)+H2O(g),

which should be inspected and compared to the one given in the question (how did sulfur enter and not get produced again?), the solid copper(II) oxide and solid copper(II) sulfide (not elemental copper) are omitted, and we only write:


Keq=[H2O]/[H2S]

Answer 2

I notice that the question asks about the RATE equation but all of the expressions in the multiple guess answers are written as possible equilibrium constants. I would venture that the correct answer is B; i.e., none of these since none of them are rate equations.