## Sapling Question #4

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HilaGelfer_2H
Posts: 91
Joined: Wed Sep 30, 2020 9:56 pm
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### Sapling Question #4

Hi,

Can anyone help me with how to approach this problem?

At a certain temperature, the given reaction has an equilibrium constant of Kp=393

PCl3(g)+Cl2(g) --> PCl5(g)

PCl5 is placed in a sealed container at an initial pressure of 0.0250 bar . What is the total pressure at equilibrium?

Alex Mele 2A
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Joined: Wed Sep 30, 2020 9:52 pm
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### Re: Sapling Question #4

I started by making an ice table from the initial partial pressures. Then, I plugged the equilibrium values into the Kp expression and solved for x. To find the total pressure at equilibrium, I added all of the partial pressures that I found together. Hope this helps!

Nathan Lao 2I
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### Re: Sapling Question #4

The first thing to do it set up an ICE box for the equation and solve for the equilibrium pressures. It's always best to solve for Q just to find out which way the reaction is proceeding. After setting up the equilibrium constant equation, you would solve for x (using the quadratic equation). Since the question asks for the total pressure of the system at equilibrium, you would add up the equilibrium pressures of each gas.

Kaitlyn Hernandez 3I
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### Re: Sapling Question #4

To start this problem, you should create an ICE table.
PCl3 Cl2 PCl5
I 0 0 0.0250
C +x +x -x
E x x 0.0250 -x

Then plug in these values in to the Kp expression to solve for X.
$Kp = \frac{P(PCl5)}{P(PCl3)P(Cl2)} = 393$

Solve for x and then plug that answer back into the equilibrium expressions from the ice table to find the concentrations for PCl3, Cl2, and PCl5. Then, add those values together to get the total pressure at equilibrium.

Mari Williams 1K
Posts: 89
Joined: Wed Sep 30, 2020 9:53 pm

### Re: Sapling Question #4

I was confused at first too, but you can use the partial pressures like a concentration and use an ICE table to solve for the pressures at equilibrium, which you can then add up :)

JasmineCap1A
Posts: 37
Joined: Wed Nov 18, 2020 12:24 am

### Re: Sapling Question #4

I think just set up the equation, create an ice table, (.025-x)/x^2=393 then do algebra to find x

Kiana Tashakori 1D
Posts: 38
Joined: Wed Nov 15, 2017 3:03 am

### Re: Sapling Question #4

Hi! To solve this, set up an ICE table using initial partial pressures, then take the resulting values and plug them into the equation Kp=(P(PCl5))/(P(PCl3)P(PCl2)). Kp is equal to 393, so you would have to plug that in as well and solve for x using a quadratic equation. The final step is to add the equilibrium pressures of the gasses together.

Sameer Chowdhury 3C
Posts: 87
Joined: Wed Sep 30, 2020 9:41 pm

### Re: Sapling Question #4

Hi! I remember getting stuck on this problem as well. After setting up the ice table and finding the partial pressures, all you have to do to find the total pressure is just find the sum of partial pressures.

abby hyman
Posts: 93
Joined: Thu Jul 25, 2019 12:16 am

### Re: Sapling Question #4

If someone could help me with this one I would be so appreciative! I have tried so many times and can't figure out what I am doing wrong so if you could use my numbers that would be great!!
Attachments

Levon Grigoryan
Posts: 25
Joined: Wed Dec 02, 2020 12:19 am

### Re: Sapling Question #4

abby hyman wrote:If someone could help me with this one I would be so appreciative! I have tried so many times and can't figure out what I am doing wrong so if you could use my numbers that would be great!!

at the end to find the answer just take the final 0.800 and subtract it 2x the number you got 0.881 and that should be the answer.

Joshua_Chan_3K
Posts: 31
Joined: Wed Nov 18, 2020 12:27 am

### Re: Sapling Question #4

First start out with the initial pressures of everything and add x values to show relative changes in pressure. The changes will be the same as the stochiometric coefficients in the reaction equation even though we are talking about pressure. You can do this using the ICE table or whatever method works best though I think the ICE table is best for visualizing. Then just plug in the numbers into the K equation to find x. After that all you need to do is use x to find each of their partial pressures and sum them together.

Jaclyn Schwartz 1I
Posts: 94
Joined: Wed Sep 30, 2020 9:45 pm

### Re: Sapling Question #4

Hi! Its so bad once you think it through. First I always set up a partial pressures. Then make an ice chart and then plug everything back into the partial pressure equation!
Kp=[pPCl5]/[pPCl3][pCl2]

ice
PCl3 + Cl2 --- PCl5
i 0 0 0.025
c +x +x -x
e x. x. 0.025-x

Kp=[0.025-x]/[x][x]=399

And solve from there! i hope that helps