What is the volume at stp of 720.0 ml of a gas collected at 20.0 °c and 3.00 atm pressure?

Combined gas law is

PV/T = K (constant)

P = Pressure

V = Volume

T = Temperature in Kelvin

For two situations, the combined gas law can be applied as,

P₁V₁ / T₁ = P₂V₂ / T₂

P₁ = 3.00 atm P₂ = standard pressure = 1 atm

V₁ = 720.0 mL T₂ = standard temperature = 273 K

T₁ = (273 + 20) K = 293 K

By substituting,

3.00 atm x 720.0 mL / 293 K = 1 atm x V₂ / 273 K

V₂ = 2012.6 mL

hence the volume of gas at stp is 2012.6 mL