Question

One liter of air at sea level contains ___ molecules.

How many molecules do 4 liters of air contain at 11 km height

Answer 1

Air pressure at 11 000 m height is 20 kPa (from a Table).

Air pressure at sea level hight is 101 kPa

One liter of air at sea level contains

( 1 L / 22.4 L/mol ) x 6.02 x 10²³ molecules/mol = 2.7x10²² molecules/L

At 11 000 m, the pressure is 1001/20=5 times lower . So will be also the number of air molecule/L air.

(Assume the temperature is the same, although it is not true).

2.7x10^22 molecules/L X 4 / (101/20) .

4 is for volume variation; 101/20 is for pressure variation. Verify the value of pressure at 11 km height in your own table.

Think to gas law: here n = pV/(RT)

Only if you consider the temperature to be 300 K at see level and 20% lower at 11 km height, n will be the same in the two cases.