Solving Partial Pressures for H2 & Cl2 given K & PHCl

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In summary, the conversation discusses the determination of K at 298K for the reaction H2(g) + Cl2(g) <---> 2HCl(g) and the equilibrium partial pressures of H2 and Cl2 when the equilibrium partial pressure of HCl is 1 bar. The formula dG*=-RTlnK is used to determine K, and the formula Pj=(xj)(Ptot) is used to determine the partial pressures. The participant also mentions using stoichiometry to solve the problem and states that they have figured it out.
  • #1
jtruth914
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a) Determine K at 298K for the reaction H2(g) + Cl2(g) <---> 2HCl(g)
b) The equilibrium partial pressure of HCl is 1 bar. Determine the equilibrium partial pressures of H2 and Cl2.


This question was on my test. I got K= 3.2 x 10^-34 using dG*=-RTlnK when dG=0 at equilibrium. I'm having trouble determining the partial pressures. I know that Pj=(xj)(Ptot). I also know that K= (PHCl)^2/(PH2)(PCl2), but I still don't know how to determine the partial pressure just based off of PHCl=1 bar?
 
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  • #2
You are most likely to assume you started with HCl and all H2 and Cl2 are products of dissociation. This, plus stoichiometry, gives you all information you need to solve the problem.
 
  • #3
I figured it out. thanks
 

What is the formula for solving partial pressures for H2 and Cl2 given K and PHCl?

The formula is P(H2) = K * P(Cl2) * P(HCl), where K is the equilibrium constant and P(HCl) is the partial pressure of hydrogen chloride.

What is the equilibrium constant (K) and how is it related to partial pressures?

The equilibrium constant (K) is a measure of the ratio of products to reactants at equilibrium. In the context of partial pressures, it represents the ratio of products (P(H2) * P(Cl2)) to reactants (P(HCl)) at equilibrium.

How do I calculate the partial pressure of hydrogen chloride (P(HCl))?

The partial pressure of hydrogen chloride (P(HCl)) can be calculated by rearranging the formula P(HCl) = P(H2) / (K * P(Cl2)).

What if I know the partial pressure of only one of the gases (P(H2) or P(Cl2))?

If you know the partial pressure of one gas, you can use the formula P(HCl) = P(known gas) / (K * P(unknown gas)) to solve for the partial pressure of the other gas.

Are there any limitations to using this formula?

Yes, this formula assumes that the gases behave ideally and that the reaction is taking place at a constant temperature and volume. It also assumes that the reaction has reached equilibrium.

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