Question

A chemical system within a sealed 1 L reaction vessel is described by the following reversible reaction equation:

2H2S(g) <---> 2H(g) + S2(g)

If the equilibrium constant is 0.000 004 200 at 1103 K find:

(a) the reaction quotient intially
(b) the order of concentration of all three components at equilibrium without using calculations
(c) what the size of the reaction quotient indicates regarding the extent of the forward reaction
(d) the quilibrium concentration of sulphur gas if 0.070 mol of hydrogen sulphide gas is intially placed in the vessel


So far I did a), b) and c) but for d) this is how much I did so far:

However, when I plug in the x value into the equation, I don't get the Keq value given to me. In other words the equation isn't LS=RS. Any help?

Thanks in adavance

Answer 1

First, I think you made a typo. I assume you meant to write
H2S ==> 2H2 + S2

Second, you need to explain to me how you obtained a,b,c without any numbers. You need numbers to calculate a reaction quotient. Why didn't you provide your answer and what you did. That way I could check it. As it is I'm in the dark as to what you did.
But here is how you do d.

..........2H2S ==> 2H2 + S2
I........0.07M......0.....0
C.........-2x.......2x....x
E........0.07-2x....2x....x

Substitute the E line into the Keq expression and solve for x = (S2)
This is a cubic equation and when I solved it I obtain about 0.0017 M for S2. I used a calculator on the web to solve the cubic. It works reasonably well I think.

Answer 2

Hello There

How I did a) was that I know that the equation for the reaction quotient was products/reactants. In this situation however, since I already have 0 moles of both products it would immediately mean that any number divided by 0 is 0.

For b), the question is also asking me to grade the concentrations from highest to lowest. So since I know that the Keq is a very small number, then that must mean that the reactants must also be a very small number. Next since it takes 2 moles of hydrogen gas for each sulfur gas, that tells me that the greatest is H2 then S2 then H2S

For c) Since I know the reaction quotient is 0 then that means that the forward reaction is very minimal or even close to not occurring.

Secondly:

For d)..... the Keq expression is [H2]^2[S2]/[H2S]^2 correct?

However, when I reach the part 4x^3/0.0049-0.28x+4x^2 I am stuck. Any help would be appreciated.