How do you determine the density of water vapor at different temperatures?
you can consider water vapor as an ideal gas , so you can write the ideal gases law
n= number of mol (n= mass in g/ MM)
R= universal costant of ideal gases
T= temperatur in K
so you can write the ideal gases law in this way
density is mass divided volume
and riarranged the equation you have
where you can see that increasing temperature, d decreases.
Moreover as the MM of water (18g/mol) is less than MM of air (about 29 g/mol), vapor has a less density tthan air