A 5.00 L container of a gas is known to contain 1.20 mol. If the amount of gas is increased to 2.80 mol, what new volume will result (at an unchanged temperature and pressure)?

Answer 1

When the temperature and pressure are constant, the combined gas law becomes

V1 / n1 = V2 / n2

V1 = initial volume = 5.00 L

n1 = initial mols = 1.2 mol

V2 = final volume = ?

n2 = final mols = 2.80 mol

5 L / 1.2 mol = X / 2.8 mol

x = 11.7 L (3 sig. figs.)

You could also look at this problem as the volume is directly proportional to the number of moles when the pressure and temperature are constant

1.2 mol = 5.0 L just as 2.8 mol = x L

2.8 mol is 2.33 x as many mols as 1.2 mol, so the volume should be 2.33 x 5.0 L

2.33 x 5.0 L = 11.7 L

Answer 2

V2= 2.8*5/1.2= 11.66L