Acetylene torches are used for welding. These torches use a mixture of acetylene
ID: 519753 • Letter: A
Question
Acetylene torches are used for welding. These torches use a mixture of acetylene gas, C_2H_2, and oxygen gas, O_2 to produce the following combustion reaction: 2C_2H_2 (g) + 5O_2(g) rightarrow 4CO_2 (g) + 2H_2O (g) Imagine that you have a 5.50 L gas tank and a 4.50 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 135 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. Express your answer with the appropriate units.Explanation / Answer
C2H2 + 2.5 O2 => 2 CO2 + H2O
Moles of O2 = 2.5 x moles of C2H2
Ideal gas equation: PV = nRT
where P is pressure, V is volume, n is moles of gas, R is molar gas constant and T is temperature in K.
n(O2) = P(O2) x V(O2)/(R x T)
n(C2H2) = P(C2H2) x V(C2H2)/(R x T)
n(O2) = 2.5 x n(C2H2)
P(O2) x V(O2)/(R x T) = 2.5 x P(C2H2) x V(C2H2)/(R x T)
135 x 5.50 = 2.5 x P(C2H2) x 4.50
P(C2H2) = 66 atm