Question

At 90C the following equilibrium is established H2(g) + S(s) = H2S(g) Kc= 6.8x10^-2
If 0.17 moles of H2 and 0.4 mole of Sulfur are heated in a 1L vessel up to 90C, what will be the partial pressure of H2S at equilibrium?
Dr. Bob, first is 0.32 atm correct? Second, if so, is 0.3 atm a better answer considering significant digits?

Answer 1

I agree with 0.322 atm and I would round that to 0.32 atm. You have two places in Kc and 2 places in 0.17. There is only 1 place in the 0.4 mol S; however, since that is a solid AND it is in excess, it never enters into the calculation so I wouldn't use that to determine the number of s.f. Congrats. You did a good job. I don't know how you solved the problem but did you notice that Kc = Kp and you can do the calculation two ways.

Answer 2

Dr. Bob, It's obvious that you're the boss. Thank-you

Answer 3

Excitement aside, how do you solve the problem using the Kp method?

Answer 4

I do understand Kc=Kp though