Question

Based on the balanced equation

2Ba + O2 → 2BaO

calculate the number of BaO formula units formed when 54 Ba atoms and 21 O2 molecules react?

Answer 1

I know I had Chemistry last year, but I'm not 100 percent sure about this answer: 21.
you need 2 atoms each of each element. Divide 54 by 2, so you get 27 Ba atoms in groups of 2. 21 is already 2 O atoms.
So you get 27 and 21. the smaller one is 21, which is the greatest amount you can get for 2BaO.

Answer 2

54 Ba atoms:
54 Ba atoms x (2 BaO molecules/2 Ba atoms) = 54 x 2/2 = 54 molecules(formula units) BaO.

21 O2 molecule:
21 O2 molecules x (2 BaO molecules/1 O2 molecule) = 42 BaO molecules.

Therefore, 42 BaO molecules will be the product formed. O2 is the limiting reagent.