# Homework Help: Chemistry - Gas Law Stiochiometry

1. Oct 3, 2007

### sam.

1. The problem statement, all variables and given/known data

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) --> 4CO_2(g) + 2H_2O(g)

Imagine that you have a 6.50 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 105 atm, to what pressure should you fill the acetylene tank to ensure that you run out of each gas at the same time?

2. Relevant equations

Boyle's Law: P_1V_1 = P_2V_2
Charles Law: V_1/T_1 = V_1/T_1
Ideal Gas Law: PV = nRT

3. The attempt at a solution
Okay, I think that I have to find temperature because then I would be able to sub that in to PV = nRT to find the number of moles for oxygen and then using mole ratio I can find the moles of acetylene and then sub that into the ideal gas law to find the pressure for acetylene. But I'm not exactly sure how to calculate temperature. Any help is greatly appreciated!

2. Oct 3, 2007

### chemisttree

Assume room temperature.