2. Given the balanced equation representing a reaction:
Zn(s) + 2HCl(aq) - H2(g) + ZnCl2(aq)
Which set of reaction conditions produces Helg) at the fastest rate?
a. a 1.0-9 lump of Zn(s) in 50 mL of 0.5 M HCl(aq) at 20."
b. a 1.0-g lump of Zn(s) in 50 ml of 0.5 M HClag) at 30.C
c. 1.0 g of powdered Zn(s) in 50. mL of 1.0 M HCl(aq) at 20.00
d. 1.0 g of powdered Zn(s) in 50. ml of 1.0 M HClag) at 30.C

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.