Nitrogen reacts with hydrogen gas to produce ammonia. What mass of
ammonia is produced when 6.50 grams of nitrogen reacts?
Atomic masses: H = 1.01; N = 14.0
a. 3.94 g
b. 7.89 g
c. 11.8 g
d. 15.8 g

Hello teatea!
The formula for an ammonia molecule is NH3. Therefore, since the
atomic mass of H is 1.01 and the atomic mass of N is 14, then the
ammonia molecular mass is 17.03. Check the following page for an
explanation of this, and a molecular mass calculator.

Molecular mass
http://www.ausetute.com.au/mmcalcul.html

Now, since there is only 1 nitrogen atom in ammonia, then we know that
for each mole of nitrogen, we will get 1 mole of ammonia. Conversely,
for every 14g of nitrogen, we will get 17.03g of ammonia. Finally,
since we have 6.5 grams of nitrogen, it's easy to find how many grams
of ammonia we'll get:

14g of N -----> 17.03g of NH3
6.5g of N ---->   X  g of NH3

Therefore, X = 17.03*6.5/14 = 7.89 g. Thus 7.89 grams of nitrogen are
produced. The correct answer is b.

Google search terms used:
"atomic mass" "molecular mass"


I hope this was clear enough. If you have any doubts, please don't
hesitate to request a clarification. Otherwise, I await your rating
and final comments.


Best wishes!
elmarto