How many molecules are in 165 g of carbon dioxide?

##2.258 xx 10^24## molecules

We use Avogadro's number of ##6.022xx10^23## molecules per mole to calculate the number of molecules from the number of moles represented by ##"165 g"## of carbon dioxide.

The gram-molecular weight of carbon dioxide can be calculated from the atomic weights for carbon and oxygen (two of them in ##"CO"_2##) given in a Periodic Table of the Elements.

##("165 g CO"_2)/("44.01 g/mol") xx (6.022xx10^23 "molecules")/"mol"##

##= \mathbf(2.258xx10^24 "molecules")##