Molecules vs moles vs Atoms?

To answer your last question first, yes, "particles" absolutely includes atoms or molecules. The relationship you wrote, mol= #of particles/ avagadros #, is used for any problem where you are going from moles to atoms or molecules, or vice versa. For example, question B above. You need to use molar mass only when going from moles ----> mass mass ----> moles atoms ----> mass mass ----> atoms molecules ----> mass mass ----> molecules In other words, any time mass is involved, for example question C above. Hope this helps a little.

a mole is a number (like a dozen or a hundred etc). the actual amount is a really big number called avogadro's number which is 6.023 * 10^23. its just easier to refer to a number of moles of something than a number of avogadro's numbers of something. being just a number, you can have a mol of atoms or molecules or even potatoes. so, you can compare b to a & d: 0.005 * 6.023 * 10^23 = 3.01 * 10^21 which you can see is bigger. grams can be converted into moles by the formula n = m/M. What this formula does is find the number of moles by dividing the number of grams of something by the number of grams of that same something when you have 1 mol of it. you can do this because a mol is conveniently chosen to be in the order of grams for most molecules you work with (exceptions being big biological molecules like proteins). so, approximating the molar mass of nitrogen as 14 and the molar mass of hydrogen as 1 (they are quite close to this) n = m/NH3 = 1/(14+1*3) = 1/17 = 0.59 moles = 0.59 * 6.02 *10^23 = 3.5 * 10^23 (remember we are dividing one gram in part C by the number of grams that are found in one mole of NH3 to find the number of moles in our one gram) hope that helped.