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 6.00 L gas tank and a 4.00 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 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

Given data ,

Volume of C2H2 = 4.00 L

Volume of O2 = 6 L

Pressure of O2 = 155 atm

Let us consider a reaction,

2C₂H₂ + 5O₂ -----> 4CO₂ + 2H₂O

From the reaction ,  1 mole C₂H₂ = 5/2 moles O₂

Let us assume ideal gas behaviour,

PV = nRT

P_C2H2 * V_C2H2 = n_c2h2* R * T---------(1)

P_O2 * V_O2 = n_O2 *R*T---------------(2)

Now, Divide eq (1) by eq (2) ,

(P_C2H2 * V_C2H2 )/(P_O2 *V_O2) = n_c2h2/ n_o2

(P_C2H2 * 4.00 L) / (6 * 155) = 2 / 5

P_C2H2 * 4.00 L = 372

P_C2H2 = 93 atm