Acetylene torches are used for welding. These torches use a mixture of acetylene
ID: 860187 • Letter: A
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 7.00L gas tank and a 4.00L 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 125atm , 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
Use the coefficients of the balanced equation.
moles of O2 using the ideal gas equation = PV/RT = 105 atm * 7 L / RT
From the balanced equation, you need 2 moles of C2H2 and 5 moles of O2 to react fully.
moles of C2H2 = 2 / 5 * 125 atm * 7 L / RT
Use the ideal gas equation again to calculate the pressure of C2H2 in the tank
n = PV/RT, substituting gives us
2 / 5 * 125 atm * 7 L / RT = P * 4 L / RT
RT is on each side so it cancels out
2 / 5 * 125 atm * 7 L = P * 4 L
Solving for P gives me 87.5 atm
Totally ignoring the fact that acetylene is way too reactive to store like this, it's stored as a solution of acetylene in acetone but that's another issue. For the purposes of your problem, this is what you want to do.