Basic Homework Help: Solving Problems with Compressed Air and Diffusion

[merrymanjane]

Can anyone help me solve these two problems?
1. A tank of compressed air of volume 1.0 m^3 is pressurized to 40 atm at T= 273. A valve is opened and air is released until the pressure in the tank is 23.0 atm. How many air molecules were released?

2. About how long will it take a perfume molecule to diffuse a distance of 7.00 m in one direction in a room if the diffusion constant is 1.00 x 10^-5 m^2/s? Assume that the air is perfectly still- there are no air currents.

 

[ShawnD]

Originally posted by merrymanjane
Can anyone help me solve these two problems?
1. A tank of compressed air of volume 1.0 m^3 is pressurized to 40 atm at T= 273. A valve is opened and air is released until the pressure in the tank is 23.0 atm. How many air molecules were released?

Use the formula
PV = nRT

P is pressure (pascals or kilopascals, I can't remember), V is volume in litres, n is the number of moles, R is the gas constant, T is temperature in kelvin
Figure out how many moles of air molecules were there at start then how much after. Just subtract the two.

 

[Moose352]

P should be in atmospheres.

 

[ShawnD]

Depends which R you use.

 

[Adrian Baker]

Use Pascals and 8.31 for R