Answer to Question #153828 in General Chemistry for Ash

Question

Helium filled balloon rises in the air because the density of helium is less than the density of air.

a. If air has an average molar of 29.0g/mol, what is the density of air at 25 and 770 mmHg?

Answer 1

for ideal gas , we have

PV = n RT

here P is the pressure of gas , V is the volume of gas , n is the number of moles of gas taken.

by putting n = 1, and by putting the values of pressure and temperature , we can find the volume of 1 mole of gas .

mass of one mole of gas is equal to the molar mass of gas . ;ets it be represented by M .

Here,

P = 770mm Hg

T= (25+273)K = 298 K

n=1

R= 62.36 L mm Hg/mol . K

putting the values in ideal gas equation ,

770 V = 1 (62.36 ) 298

V = 24.13 L

To solve this question , we are assuming ideal gas behaviour and so ideal gas equation is applicable for all the gases given here .

meaning , one mole of every gas (air,helium,carbon dioxide) will occupy 24.13L at the given conditions

a). mass of one mole gas = 29g

density of gas = $\frac{Mass}{Volume}$ = $\frac{29g}{24.13L}$

= 1.2 g/L