Acetylene torches are used for welding. These torches use a mixture of acetylene

Question

Acetylene torches are used for welding. These torches use a mixture of acetylene gas, C2H2, and oxygen gas, O2 to produce the following combustion reaction: 2C2H2(g)+5O2(g)4CO2(g)+2H2O(g)

Imagine that you have a 7.00 L gas tank and a 3.00 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 115 atm , to what pressure should you fill the acetylene tank to ensure that you run out of each gas at the same time? Assume ideal behavior for all gases.

Explanation / Answer

The balanced reaction is :-

2C2H2(g) + 5O2(g) ------> 4CO2(g) + 2H2O(g)

Molar ratio in which acetylene and oxygen reacts = 2:5

Now,

Applying Ideal Gas Equation ; i.e. P*V = n*R*T

moles of oxygen stored in the cylinder = (P*V)/(R*T) = (115*7)/(0.0821*298) = 32.903

Thus, moles of acetylene required to be stored = (2/5)*moles of oxygen stored = 13.161

Applying Ideal gas equation, we get

P = (n*R*T)/V = (13.161*0.0821*298)/3 = 107.334 atm

Hence., acetylene needs to be stored at a pressure of 107.334 atm

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