You are driving west on highway 510 in a european car. the speed limit for this portion of the highway is 50 miles per hour. your speedometer reads 120 km/hr. are you speeding or not? how fast are you traveling in mph? (1 km =0.621 miles)

Divide 50 miles an hour or mph by 0.621, should give you 80.51 kilometers an hour or km/hr, this being the speed limit on that street in km/hr. If you're going 120 km/hr on an 80.51 kilometers an hour road you are speeding, as you're above the speed limit.

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.

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