Hello, Isabel,

The problem notes that our gas occupies 380.8 liters at STP. Any gas at STP occupies 22.4 liters/mole of that gas. We're at STP, so 380.8 liters means we have (380.8 liters)/(22.4 liters/mole)= 17 moles of the gas.

Now use the ideal gas law:

PV = nRT, where P and V are pressure and volume, n is the number of moles, R is the ideal gas constant, and T is the temperature (in Kelvin).

Rearrange this to find pressure, set up a table for the values, and calculate:

P= nRT/V

Cancel the units carefully. You will wind up with just pressure. The gas constant I used has pressure expressed as atm, so that will be the unit for final pressure, 5.34 atm.

Bob