Calculate the number of moles of o2 gas held in a sealed, 2.00-l tank at 3.50 atm and 25.0°c. how many moles would be in the tank if the temperature was raised to 49.0°c and the pressure remained constant (trick question) ?

It's an ideal gas problem:

first, we will use this formula to get V2:

P1V1/T1 = P2V2/T2

when the Pressure still constant:

∴ V1/T1 = V2 / T2

when V1 = 2 L

T1 = 25 °C

T2 = 49°C

∴2 L / 25°C = V2 / 49

∴V2 = 3.92 L

then we will use this formula to get no. of moles:

P2V2 = nRT

when P2 = P1 = 3.5 atm

V2 = 3.92

R = 0.0821

T2 = 49°C + 273 = 322 K

by substitution:

∴3.5 atm * 3.92 L = n * 0.0821 * 322 K

∴n = 0.5 mol

∴ no. of moles = 0.5 mol