So if we wait a minute, our lungs exchange six liters of air. Now, the question is how many molecules are found within six liters of air assuming we're at room temperature and at atmospheric pressure so how many molecules does this represent at room temperature? At a temperature of about 21 degrees Celsius and a pressure of about one atmospheric pressure, one ATM. So to calculate the number of molecules exchanged by the lungs every single minute we have to calculate the number of moles of air that is exchanged and to calculate the moles we can use the ideal gas law. So n is equal to where n is our number of moles is equal to the pressure in ATM multiplied by the volume in liters divided by the gas constant r multiplied by the temperature given to us in Kelvins. Now, the pressure we're assuming is one ATM the volume we calculated to be six liters the ideal gas law is 0.20.81 ATM times liter divided by kelvin times mole and the temperature in Kelvin is equal to 21 plus 273 and that gives us about 294 Kelvins.