Chem Equil: CH4 + H2S -> CS2 + H2 - Calc \[CS_2\] at Equil

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The discussion revolves around calculating the equilibrium concentration of CS2 in the reaction CH4 + 2H2S <-> CS2 + 4H2, given an equilibrium constant (k_eq) of 100 and specific amounts of reactants at equilibrium. Participants express confusion over the problem's wording, particularly regarding the definition of "reactants" versus "substrates." After clarifying the initial amounts and applying the equilibrium formula, it is determined that the concentration of CS2 at equilibrium is 0.323 mol. The conversation highlights the importance of precise terminology in chemistry problems. Overall, the participants successfully navigate the problem to arrive at the correct equilibrium concentration.
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Reaction: CH_4 + 2H_2S &lt;-&gt; CS_2 + 4H_2
k_{eq} = 100 at a certain temperature

An unkown amount of reactants were intorduced into a 1.0L bulb and at equilibrium 0.10 mol of CH_4 and 0.30 of H_2S were found. Calc \[CS_2\] at equilibrium.

I don't seem to have enough information here. I can form the equation for k_{eq} but I have two unknowns...
 
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Lousy problem statement: the idiot who wrote it mentally equates "reactants" with materials on "left-hand side of equation." Help?
 
Reactants or substrates? If reactants, there is no way to solve the question. If substrates, it is easy.

Two unknowns - you mean amounts of CS2 and H2?

Oops, Bystander was faster :)
 
cscott I tried to resolve this. But before I show how I think this might be done, I want to make sure that I am right. Is the amount of \[CS_2\] at equilibrium 0.323 mol ?
 
Bystander said:
Lousy problem statement: the idiot who wrote it mentally equates "reactants" with materials on "left-hand side of equation." Help?

That idiot would be me :rolleyes:. Sorry.

Reactants or substrates? If reactants, there is no way to solve the question. If substrates, it is easy.

I've never heard of "substrates" before. We just barely learned that the reactions go both ways :-p, so I guess that's why I associated reactants with the LHS.

Two unknowns - you mean amounts of CS2 and H2?

Yes.

But before I show how I think this might be done, I want to make sure that I am right.

I didn't get the answers for this practice sheet yet. Maybe you can show your method anyway?
 
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cscott said:
That idiot would be me :rolleyes:. Sorry. (snip)

Huh? You didn't write the problem, you're trying to solve it. All I was doing was translating what was meant by "reactants" as a hint for you.
 
Bystander said:
Huh? You didn't write the problem, you're trying to solve it. All I was doing was translating what was meant by "reactants" as a hint for you.

The problem originally stated the two molecules on the LHS instead of "reactants". I was just being lazy.

I'm still not sure how to get the concentration of H_2 at equilibrium to in turn get it for CS_2
 
I didn't get the answers for this practice sheet yet. Maybe you can show your method anyway?

Ok. Here it goes.

First, let's identify the initial amount of the various substances, reactants and products:
CH4 -> n mol
H2S -> m mol
CS2 -> 0 mol
H2 -> 0 mol

At equilibrium according to the stoichiometric coefficients of the substances their amount should be:
CH4 -> n - x mol
H2S -> m - 2x mol
CS2 -> x mol
H2 -> 4x mol

Nevertheless, the problem gives us the amount at equilibrium of CH4 and H2S which are respectively 0.10 mol and 0.30 mol.

Then, we must apply the chemical equilibrium formula using the equilibrium constant given by the problem:

100 = x(4x)^4) / (0.10 x 0.30^2)

Now, it's math.
x will be equal to 0.323 mol

Hope I could help.
 
Thanks PPonte.
 

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