Question

Acetylene torches are used for welding. These torches use a mixture of acetylene gas, C 2 H 2 , and oxygen gas, O 2 to produce the following combustion reaction: 2 C 2 H 2 (g)+5 O 2 (g)→4C O 2 (g)+2 H 2 O(g)

Imagine that you have a 5.00 L gas tank and a 3.50 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 155 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.

Answer 1

According to the equation 2 moles of acetelene requires 5 moles of oxygen for perfect welding acetelene torch.

Ideal gas equation

pV = nRT

R and T are same for both gases.

ACETELENE

For acetelene pressure(p1) = ?

volume of acetelene = 3.5 L

number of moles to be run = 2

OXYGEN

For oxygen pressure(p2) = 155 atm

volume of oxgen = 5 L

number of moles to be run = 5

Equate both so that we have ,

(p1 x 3.5 L) / 2 moles =    (155 atm x 5 L) / 5 moles

so pressure of acetelene to be = 155 atm x 2/3.5

= 88.57 atm.