Question

What is the principle of atom conservation? Explain with an example.

Answer 1

The Principle of Atom Conservation (POAC) states that the total number of atoms of reactants must equal the number of atoms of products.

Explanation:

The POAC comes from the Law of Conservation of Mass.

`"Mass of atoms of element in reactant"color(white)(l) =color(white)(l) "mass of atoms of element in product"`

`"Number of atoms of element in reactant"color(white)(l)`
`= color(white)(l)"number of atoms of element in product"`

`"Moles of atoms of element in reactant" color(white)(l)=color(white)(l)"moles of atoms of element in product"`

You do not need a balanced equation to solve a stoichiometry problem by the POAC method.

EXAMPLE

What mass of `"O"_2` is produced by 1.23 g of `"KClO"_3`?

Solution

The unbalanced equation is

`"KClO"_3 → "KCl" + "O"_2`

`"1 mol KClO"_3` contains `"3 mol O atoms"`; `"1 mol O"_2` contains `"2 mol O atoms"`.

So

`"3 × mol KClO"_3 = "2 × mol O"_2`

`"Moles of O"_2 = 3/2 × "mol KClO"_3`

So we can calculate the moles of `"KClO"_3`, then convert to moles of `"O"_2` and finally to grams of `"O"_2`.

`"Moles of KClO"_3 = 1.23 cancel("g KClO₃") × ("1 mol KClO"_3)/(122.55 cancel("g KClO₃")) = "0.010 04 mol KClO"_3`

`"Moles of O"_2 = "0.010 04" cancel(color(black)("mol KClO"_3)) × "3 mol O"_2/(2cancel(color(black)("mol KClO"_3))) = "0.015 06 mol O"_2`

`"Mass of O"_2 = "0.015 06" cancel("mol O₂") × ("32.00 g O"_2)/(1 cancel("mol O₂")) = "0.482 g O"_2`

Answer 2

To put this in another way, the principle of conservation of mass insists........

Explanation:

.....that mass is conserved in every chemical reaction. That is, if you start with `10*g` of reactants from all sources, AT MOST, you can get `10*g` of products. That atoms and molecules certainly have definite, and measurable masses supports this proposition.

And the evidence....well, for every chemical reaction EVER performed, the mass of products, equals the mass of reactants. And thus `"garbage out equals garbage in"`. In practice, losses always occur on handling, and so usually, the garbage out is slightly less than the garbage in.