A room measures 3m*5m* 5m.Approximately how many molecules of air are in the room ?

Question

A room measures 3m*5m* 5m .Approximately how many molecules of air are in the room ? Take room temperature to be 25degrees and the pressure to be 1.0×105Pa , and Boltzmann's constant to be 1.38×10−23JK^-1 . Remember to convert the temperature to Kelvin.


Question 2
Air at atmospheric pressure (1.0×105 ) is compressed at constant temperature in a bicycle pump so that its volume is reduced by a factor of 8.
a) What is the pressure of the air when compressed ?
b) What is the area of the piston in the pump, if the force acting on it is 103N ?give your answer in square metres.
c) If the pressure is sufficient to open the valve but not to pump air into the tyre, what is the pressure in the tyre ?Give your answer in Pascals.

D g · Accepted Answer

at STP i think  6.022*10^23 moles of gas is in  22.4 L 

but STP is 0 degs  C 

at 25 degs C this will be different

use Ideal gas law

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/idegas.html

PV = nKT

where K = boltsman constant

solve  for n

n = KT/ PV

volume of the room is   3* 5*5 = 75 m^3

T = 273.15 + 25 = 298.15 

sorry  you should get a bit of a head start using that...

then remember each mole will have 6.022 * 10^23 moles  so multiply by that to get the number of molecules

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A room measures 3m5m 5m.Approximately how many molecules of air are in the room ?

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