According to the balanced reaction below, calculate the moles of NH3 that form when 4.2
mol of NzH4 completely reacts
3 N2H4(1)
4
NH3(g) + N2(g)

Easy moles to mass conversion :)

So, the first step would be our "given" over 1. Our given, is 0.427.

So, our first step would look like this:

0.427 mol He

         1

For our second step, we need to cancel out moles. So, we would put one mole on the bottom of our second step, to cancel out. Whenever we use the periodic table to find molar mass in a conversion, it is ALWAYS one mole. To find grams, we will simply calculate the molar mass of helium, which is 4.003 (atomic mass on the periodic table)

Our second step would look like this:

4.003g He

   1mol He

So, when we put the two steps together, it looks like this:

0.427mol He    4.003g He
x
         1              1mol He

To find our answer, we: 
Multiply the top numbers together (we get 1.709281)
Multiply the bottom numbers together (we get 1)

Then, we divide the top product together by the bottom product together. 

1.709281/1

Our answer is 1.709281

So, from 0.427 moles of Helium, we get 1.709281 grams of Helium.