Question

A flask contains 2.0 mol of He gas at 25°C and 1.00 atm. How much He gas, in grams, must be added to increase the pressure to 2.00 atm at constant temperature and volume?

Answer 1

Mass of He required = 8.0 g

Step-by-step explanation:

Given,

Initial moles of He = 2.0 mol

Initial pressure = 1.00 atm

final pressure = 2.00 atm

Ideal gas equation,

PV = nRT

As V, R and T are constant

So,
`(P_1)/(P_2) =(n_1)/(n_2)`

`(1.00 atm)/(2.00 atm) =(2.0)/(n_2)\\n_2=(2.0* 2.00)/(1.00) \\n_2=4.0 mol`

Molar mass of He = 4.00 g/mol

No. of moles of He needs to be added = 4.0 - 2.0 = 2.0 mol

Mass = No. of mole × Molar mass

= 2.0 × 4.0

= 8.0 g