TBR Gen Chem Equilibrium passage IV

[vashka]

ACK! I don't get this passage at all! So, 0.8atm H2 goes in...how do we know that total pressure can never reach a value as low as 0.6atm? Or that 0.2atm of CS2 was initially added?

The Passage reads:
During an experiment, the closed glass cylinder is filled with 1.00 atm. of hydrogen (H2) according to the gauge in the cylinder. Flask I is filled with 1.0 atm carbon disulfide
(CS. The reaction starts when the stopcock is opened allowing the two gases to mix. The temperature of the glass column is maintained at 25"C using an external heat sink.
The internal pressure is monitored until it stays constant Figure 2 shows the internal pressure over time, where t = 0 represents the time at which the two gasses were mixed.

The pressure of each gas in the reaction mixture can be calculated from the change in internal pressure. The initial partial pressure of hydrogen gas is 0.8 atmospheres in the
l.25 L closed system. The decrease in partial pressure of hydrogen gas is double the decrease in the internal pressure based on the stoichiometry of the Reaction 1, which shows the reactivity of the compounds.

1 CS2(g) + 4H2(g) =: 1 CH4(g) + 2 H2S(g)
Reaction 1

The final internal pressure is the sum of the partial pressures.

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[vashka]

Disregard I now totally understand it. Thanks to anyone who checked out the question!

 

[greenseeking]

Disregard I now totally understand it. Thanks to anyone who checked out the question!

Hi I was actually confused on the same problem. could you please explain how you figured it out?

thanks!

 

[vashka]

We know 0.2atm of CS2 was added b/c H2 and CS2 react in a 4:1 ratio and 0.8atm of H2 was initially in the container.

So we start with 0.2atm of CS2. During the reaction we cannot lose more CS2 than we had initially. So, at equilibrium, concentration of CS2 will be 0.2-x. X cannot be greater than 0.2. We also know that total pressure cannot be less than 0.6 because total pressure is 1-2x. If X has to be less than 0.2, then 1-2x cannot be more than 0.6atm

Hope this helps!

 

[JLeBling]

Maybe my brain is broken right now...

But for number 25. Where:

Ptotal = PCS2 + PH2 + PCH4 + PH2S
= 1-2x= (0.2-x) + (0.8-x) + (x) + (2x)

I'm not completely certain as to why:
Ptotal = 1-2x

The answer book says it's because of the 4:1 Reactant vs. 2:1 Product ratio.

I am fairly certain it has something to do with what it says in the passage: "the decrease in partial pressure of hydrogen gas is double the decrease in the internal pressure based on the stoichiometry of reaction 1"

Which is
1 CS ___+ 4 H _____---> 1 CH + 2H S
___2 (g) ____2 (g) <--- _____4(g) ____2 (g)

For some reason it isn't registering in my head...... Help!

 

[JLeBling]

5:3 molar ratio... is that it?

 

[gkdubey]

bump

 

[gkdubey]

Sorry but I have same question. How in the world is it 2x-1 for product? I hope someone will see this and answer both our questions

 

[gkdubey]

Never mind...I figured it out...Sorry to bring this back from the dead

 

[1TB4RKSB4CK]

Maybe my brain is broken right now...

But for number 25. Where:

Ptotal = PCS2 + PH2 + PCH4 + PH2S
= 1-2x= (0.2-x) + (0.8-x) + (x) + (2x)

I'm not completely certain as to why:
Ptotal = 1-2x

The answer book says it's because of the 4:1 Reactant vs. 2:1 Product ratio.

I am fairly certain it has something to do with what it says in the passage: "the decrease in partial pressure of hydrogen gas is double the decrease in the internal pressure based on the stoichiometry of reaction 1"

Which is
1 CS ___+ 4 H _____---> 1 CH + 2H S
___2 (g) ____2 (g) <--- _____4(g) ____2 (g)

For some reason it isn't registering in my head...... Help!

There has to be an easier way, or at least an intuitive approach, that's just too much math for one question lol

 

[snllama]

I'm not completely certain as to why:
Ptotal = 1-2x

Im stuck on this problem right now. I guessed the right answer due to inferring from the passage that PH2=2x(change in P). I was able to set up the partial pressures, but I dont get where the 1-2x came from.

Anyone?