Question

12. What is the pressure in a 1.00 liter container of methane, CH4,(Molar mass= 16 g/mol) that contains 40.0 g of the gas at 25.0°C? A) 5.13 atm B) 61.0 atm C) 82.1 atm D) 979 atm E) 3,920 atm 13. What is the total pressure of a mixture of He and H2 if the partial pressures are 320 mm Hg and 800 mm Hg respectively? A) 40 mm Hg B) 60 mm Hg C) 320 mm Hg D) 480 mm Hg E) 1120 mm Hg

Answer 1

12)

Molar mass of CH4,

MM = 1*MM(C) + 4*MM(H)

= 1*12.01 + 4*1.008

= 16.042 g/mol

mass(CH4)= 40.0 g

use:

number of mol of CH4,

n = mass of CH4/molar mass of CH4

=(40 g)/(16.04 g/mol)

= 2.493 mol

Given:

V = 1.0 L

n = 2.4935 mol

T = 25.0 oC

= (25.0+273) K

= 298 K

use:

P * V = n*R*T

P * 1 L = 2.4935 mol* 0.08206 atm.L/mol.K * 298 K

P = 61.0 atm

Answer: B

13)

Total pressure = p(He) + p(H2)

= 320 mmHg + 800 mmHg

= 1120 mmHg

Answer: E