Question

A tube containing nitrogen gas at 25 c is evacuated till pressure is .02mm of hg.find the number of nitrogen molecules still present in the tube if volume of tube is 2 lit?

Answer 1

Pressure, P=0.02mm Hg(given)

1mm Hg= 0.00132 atm

0.02mm Hg= 0.0000264 atm

Volume, V= 2 lt(given)

Temp, T= 25C = 298 K

As we know, PV= nRT so n= PV / RT (substituting values in this equation)

n= (0.0000264 x 2)/ (8.314 x 298) = 2.13 x 10^ -3 moles

1 mole of nitrogen contains 6.022 x 10^23 molecules

2.13 x 10^ -8 moles of nitrogen contains( 6.022 x 10^23 ) X ( 2.13 x 10^ -8) molecules

= 12.827 x 10^15 molecules.