Chemistry: gas equations, mole, volume and pressure

Question

A sample of O2 with a pressure of 220mmHg contains 2.0 moles of gas and has a volume of 4.0L. What will the new pressure be when the volume expands to 5.0L and 3.0 moles of He is added while temperature is constabt?

Answer 1

At constant temperature and a change in the number of moles, you can use P1V1/n1 = P2V2/n2 and solve for P2

P1 = 220 mm Hg

V1 = 4.0 L

n1 = 2.0 moles

P2 = ?

V2 = 5.0 L

n2 = 3.0 moles

P1V1n2/V2n1 = P2

P2 = (200)(4.0)(3.0)/(5.0)(2.0)

P2 = 240 mm Hg