December 03, 2021, 08:03:53 PM
Forum Rules: Read This Before Posting


Topic: KP calculation  (Read 18298 times)

0 Members and 1 Guest are viewing this topic.

chemical

  • Guest
KP calculation
« on: May 07, 2005, 10:33:07 AM »
hi, i,m  a newbie to the forum as you can see have been searching for a chemistry forum for a while now and this seems pretty active and good compared to others.  :)

ok lets see how smart this place is i have worked out a KP calcuation for the following reaction but i am not too sure if its correct, so could some1 try and answer the following question

at 1600 oC  and 1.5 atm pressure NO is 99% dissociated at equilbrium. calculate the value of Kp under these condition.

2NO <------> N2 + O2  all in gase phase

Offline Donaldson Tan

  • Editor, New Asia Republic
  • Retired Staff
  • Sr. Member
  • *
  • Posts: 3177
  • Mole Snacks: +261/-13
  • Gender: Male
    • New Asia Republic
Re:KP calculation
« Reply #1 on: May 07, 2005, 05:30:08 PM »
this is a relatively easy question, but we still adhere to the forum policy that you must show that you have the tried the problem
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

chemical

  • Guest
Re:KP calculation
« Reply #2 on: May 07, 2005, 06:10:08 PM »
hi, ok this is what i did to get my answer:

i got 66.7 (no units).

the starting moles i did 2moles of NO, and zero for both N2 and O2

and at equilbrium they wer 0.01  0.4975   0.4975

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26864
  • Mole Snacks: +1742/-403
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re:KP calculation
« Reply #3 on: May 07, 2005, 08:35:02 PM »
and at equilbrium they wer 0.01  0.4975   0.4975

Not 0.01 0.495 0.495?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

chemical

  • Guest
Re:KP calculation
« Reply #4 on: May 08, 2005, 07:09:33 AM »
Quote
Not 0.01 0.495 0.495?


NO scrap what i said before i did a mistake i should have assumed there was 1 mole rather then write 2 moles.

at equilbrium there wil be NO2 = 0.01  and N2=0.2475  O2= 0.2475

total moles= 0.505
mole fraction: NO2= 0.0198      N2= 0.4901         O2= 0.4901
Pa at 1.5 atm=        0.0132             0.3267                 0.3267


p(0.3267)*p(0.3267)
-------------------------
p(0.0132)2         =612.6 (no units)


pleaaaaaaase could you check if this answer is correct.
May i get a scooby snack if i am correct  ;D
« Last Edit: May 08, 2005, 07:10:33 AM by chemical »

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26864
  • Mole Snacks: +1742/-403
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re:KP calculation
« Reply #5 on: May 08, 2005, 07:38:14 AM »
NO scrap what i said before i did a mistake i should have assumed there was 1 mole rather then write 2 moles.

In this case everything cancels out and equlibrium constant can be calculated using either partial pressures or numbers of moles as they are directly proportional.

Start with 1 mole as you did at first. You will have 0.01 mole NO left at equilibrium. Now you have to carefully calculate amount of N2 and O2 at equilibrium.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

chemical

  • Guest
Re:KP calculation
« Reply #6 on: May 08, 2005, 07:57:47 AM »
In this case everything cancels out and equlibrium constant can be calculated using either partial pressures or numbers of moles as they are directly proportional.

Start with 1 mole as you did at first. You will have 0.01 mole NO left at equilibrium. Now you have to carefully calculate amount of N2 and O2 at equilibrium.

hmmm should i get a new calculator i keep getting wrong calculation answers i had this 1 for over 7 years lol.

well this is what i did 0.01/2=  0.005/2= 2.5 X 10-3

therefore the answer would be 0.063 (no units)


correct??

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26864
  • Mole Snacks: +1742/-403
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re:KP calculation
« Reply #7 on: May 08, 2005, 09:11:02 AM »
hmmm should i get a new calculator i keep getting wrong calculation answers i had this 1 for over 7 years lol.

For such simple questions I am using calculator that is over forty now ;)

Quote
well this is what i did 0.01/2=  0.005/2= 2.5 X 10-3

No. If you have started with 1 mole NO and there is 0.01 mole NO left, how much moles of N2 and O2 have beed produced?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

chemical

  • Guest
Re:KP calculation
« Reply #8 on: May 08, 2005, 10:52:22 AM »
For such simple questions I am using calculator that is over forty now ;)No. If you have started with 1 mole NO and there is 0.01 mole NO left, how much moles of N2 and O2 have beed produced?
0.99/2 = 0.495  

but i though when it said 0.99 disociated it means that this amount didnt react?

chemical

  • Guest
Re:KP calculation
« Reply #9 on: May 09, 2005, 06:40:16 AM »
my answer is correct?

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7982
  • Mole Snacks: +555/-93
  • Gender: Male
Re:KP calculation
« Reply #10 on: May 09, 2005, 09:56:48 AM »
No, it should be (0.495)^2/(0.01)^2
AWK

huh?

  • Guest
Re:KP calculation
« Reply #11 on: May 20, 2005, 01:19:38 PM »
hi,

i dont understand how you came to that answer, this is what i did.

                                  2NO<-->       N2     +             02                        TOTAL
 

intial                           1.00              0                       0

equilbrium  
(99%dissociated)             0.01         4.67X10^-3         5.34 X10^-3         0.02

mole fraction        0.01/0.02=0.5         0.2335                  0.267

partial pressure at            
1.5 atm                  1.5x0.5= 0.75        0.35025               0.4005


KP=  0.140275125/ 1.5

kp= 0.09 (NO UNITS)

Offline Donaldson Tan

  • Editor, New Asia Republic
  • Retired Staff
  • Sr. Member
  • *
  • Posts: 3177
  • Mole Snacks: +261/-13
  • Gender: Male
    • New Asia Republic
Re:KP calculation
« Reply #12 on: May 20, 2005, 04:47:58 PM »
let N be initial number of moles of NO

given we have 99% dissociation,
mole of NO =  0.01N
mole of N2 = 0.99N/2 = 0.495N
mole of O2 = 0.99N/2 = 0.495N

total number of moles = 1.00N

using Dalton's Law of Partial Pressure,
partial pressure of N2 = 0.495N/(1.00N) * 1.5atm = 0.7425atm
partial pressure of O2 = 0.495N/(1.00N) * 1.5atm = 0.74125atm
partial pressure of NO = 0.01N/1.00N * 1.5atm = 0.015atm

Kp = (0.7425atm)2/(0.015atm)2 = 2450
« Last Edit: May 23, 2005, 08:08:05 PM by geodome »
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 26864
  • Mole Snacks: +1742/-403
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re:KP calculation
« Reply #13 on: May 22, 2005, 02:56:59 PM »
let N be initial number of moles of NO

given we have 99% dissociation,
we have 0.01N of NO, 0.99N of N2 and 0.99N of O2

Have you taken into account the fact that O2 and N2 are diatomic particles?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Sponsored Links