Chemists use the mole as the unit for the amount of substance. One mole is equal to 6.02 x 10^23 (just like one dozen is equal to 12). A 40.1 g sample of calcium contains approximately 1 mole of calcium atoms. How many calcium atoms are in a 4 kg sample of calcium?

Explanation:

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In this case, since we are given 4 kg of a calcium-containing sample, in order to compute the atoms there first need to compute the mass in grams:

Next, via the molar mass and the Avogadro's number, we can compute the atoms as follows:

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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.

sry but any answer choices