Question

A 97.8 g sample of O2 gas at 0.0 oC and 380 Torr is compressed and heated until the volume is 4.00 L and the temperature is 27 oC. What is the final pressure in Torr?

Answer 1

step 1: calculate initial volume

Molar mass of O2 = 32 g/mol

mass(O2)= 97.8 g

use:

number of mol of O2,

n = mass of O2/molar mass of O2

=(97.8 g)/(32 g/mol)

= 3.056 mol

Given:

P = 380 torr

= (380/760) atm

= 0.5 atm

n = 3.0562 mol

T = 0.0 oC

= (0.0+273) K

= 273 K

use:

P * V = n*R*T

0.5 atm * V = 3.0562 mol* 0.08206 atm.L/mol.K * 273 K

V = 136.9 L

step 2: find final pressure

Given:

Pi = 380 torr

Vi = 136.9 L

Vf = 4.00 L

Ti = 0.0 oC

= (0.0+273) K

= 273 K

Tf = 27.0 oC

= (27.0+273) K

= 300 K

use:

(Pi*Vi)/(Ti) = (Pf*Vf)/(Tf)

(380 torr*136.9 L)/(273.0 K) = (Pf*4 L)/(300.0 K)

Pf = 14292 torr

Answer: 1.43*10^4 torr