How many molecules are in 3.78 moles of PCL3

I'm not getting this.

You know Avagadro's number 6.02 x 10^23 atoms in one mole. And you have 3.78 moles.
Now it's just unit analysis...
3.78 moles PCl3 x ((6.02 x 10^23 molecules)/1 mol).
Moles will cancel, giving you an answer in molecules, which is what you want.

I got 2.276 x 10^24 molecules.

Hope this helps.

In counting eggs, when you reach 12, you call it a dozen. In counting molecules, when you reach 6.02x10^23, you call it a mole. Moles are just a counter for a very large number of particles (atoms, molecules, ions, etc). In counting pennies, when you reach 100 you have a dollar.

? PCl3 molecules = 3.78 moles PCl3 x 6.02x10^23 PCl3 molecules / 1 mole PCl3
= 22.8x10^23 = 2.28x10^24 PCl3 molecules