When zinc metal reacts with oxygen gas, 2Zn(s) + O2(g) → 2ZnO(g), large amounts of light and heat are released. A student states that this reaction is a combustion reaction but not a redox reaction. Do you agree? Defend your answer by explaining whether or not it meets the requirements of each type of reaction. (6 points)

A neutral element on its own in its standard state has an oxidation number of zero.

The sum of the oxidation numbers for a neutral molecule must be zero.

The sum of the oxidation numbers for an ion is equal to the net charge on the ion.

In a compound or simple ion: group 1 metals are always +1, group 2 metals are always +2.

In a compound: other metals (not group 1 or 2) prefer a positive oxidation state.

In a compound: hydrogen prefers +1, oxygen prefers -2, fluorine prefers -1.

In a compound with no oxygen present the other halogens will also prefer -1.

Explanation:

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.