[NighStalker]

Hey guys, I am having a lot of difficulty with these 2 problems, if anyone can help me out, by providing, the answer, hints, solution, or method of solving these problems, it would be greatly appreciated!

1) 2C2H2(g) + 5O2(g) --> 4CO2(g) + 2H20(g)
Imagine that you have a 6.30 L gas tank and a 4.15 L gas tank. You need to fill one tank with oxygen and the other with acetylene to use in conjunction with your welding torch. If you fill the larger tank with oxygen to a pressure of 140 atm, to what pressure should you fill the acetylene tank to ensure that you run out of each gas at the same time?

2) A 2.55 L container of H2(g) at 745 mmHg and 22 degrees C is connected to a 3.16L container of He(g) at 730 mmHg and 22 degrees C.
--After mixing, what is the total gas pressure, in millimeters of mercury, with the temperature remaining at 22 degrees C?

[Borek]

PV=nRT for both questions.

In the first - calculate number of moles of oxygen, then stoichiometric number of moles of acetylene.

In the second - calculate number of moles of each gas, add them to get total number of moles, then use total moles and total volume to calculate new pressure.

[NighStalker]

Thanks a lot Borek. Especially for giving me the method instead of just the answers

[NighStalker]

I am trying question 1, and i got P=590 atm but it was wrong
i also somehow got 943 and 293 atm which were wrong, can someone confirm what the correct answer is for the first question?

[thelegace]

PV=nRT for both questions.

In the first - calculate number of moles of oxygen, then stoichiometric number of moles of acetylene.

In the second - calculate number of moles of each gas, add them to get total number of moles, then use total moles and total volume to calculate new pressure.

I get a pressure value of 123.565 atm, using values from the thread I made, which were volume O2 = 7L, volume C2H2 = 4.5L and Pressure oxygen 145atm.  I figure this is the total pressure maybe? But it's still lower than the pressure of oxygen, I would expect the pressure of acetylene to be much higher considered in has a lot less volume.

Thanx.

[NighStalker]

that doesnt really help me, i have tried a lot of different ways, and at this point i was wondering if anyone could guide me through the solution of question 1, since i attempted it 3 times and got it wrong!

[NighStalker]

nvm i got the right answer, it was 94.3 and i was readin my calc wrong

[Borek]

Strange, I got 85 atm for the first question.

How many moles of oxygen?

How many moles of acetylene?

[Borek]

Note: this question can be solved very easily without even calculating number of moles of neither substance.

n_oxygen=P_oxygenV_oxygen/(RT)

n_acetylene=P_acetyleneV_acetylene/(RT)

and from the reaction equation we know that

2n_oxygen = 5n_acetylene

RT cancels out and we are left with one unknown only.

[NighStalker]

borek we are both correct, my numbers we slightly off from the numbers posted, because i wanted to make sure that I could solve the prob myself, and wouldnt  be tempted to copy someone elses answer (that used the values i give above which are diff than mine)