Kp values and partial pressure

Announcements
    • Thread Starter
    Offline

    2
    ReputationRep:
    Hello everyone,

    I am stuck on the last question of the worksheet attached. I keep on getting a value of 22.5 KPa, but the answer is 80 KPa.

    I got my answer algebraically - at the start the moles of hydrogen and iodine are X, and at eqm there's 1.5 moles of iodine. Therefore, the change in iodine is -(X-1.5), which is the same for the hydrogen) This also implies HI has increased by 2(x-1.5), giving that many moles at eqm, along with X-(X-1.5) moles of hydrogen.

    Are my terms correct - because then I put it in the Kp formula.

    Can anyone help?
    Attached Files
  1. File Type: doc Topic 11 Exercise 4 - Kp (1).doc (30.5 KB, 28 views)
    Offline

    2
    ReputationRep:
    Nice Q, made me think for a moment.

    Your mathematics are all fine. The thing you're missing is the information given to you by the Kp value.

    Kp = pp(HI)2 / (pp(H2) x pp(I2))

    = (Ptot x n(HI)/ntot)2 / ((Ptot x n(H2)/ntot) x (Ptot x n(H2)/ntot))

    The 2x Ptot and ntot cancel out top and bottom, leaving you with

    = n(HI)2 / n(H2) x n(I2)

    At equilibrium, we know what n(H2) and n(I2) are, so can work out n(HI) and the rest falls into place.
    • Thread Starter
    Offline

    2
    ReputationRep:
    Thanks for the help.
 
 
 
Write a reply… Reply
Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: October 1, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Poll
Would you prefer to be told about sex by your:
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.