The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction. This can be gleaned from the third postulate in Dalton's series. Magnesium oxide decomposes into magnesium and oxygen. If 16.12 g of magnesium oxide decomposes to form 9.72 g of magnesium, what mass of oxygen gas is also released in the reaction?

Law of conservation of mass : It states that mass can neither be created nor be destroyed but it can only be transformed from one form to another form.

This also means that total mass on the reactant side must be equal to the total mass on the product side.

The balanced chemical reaction will be,

[tex]2MgO\rightarrow 2Mg+O_2[/tex]

According to the law of conservation of mass,

Total mass of reactant side = Total mass of product side

Total mass of [tex]2MgO[/tex] = Total mass of [tex]2Mg+O_2[/tex]

or,

Total mass of [tex]2MgO[/tex] = Mass of [tex]2Mg[/tex] + Mass of [tex]O_2[/tex]

As we are given :

Total mass of [tex]MgO[/tex] = 16.12 grams

The mass of [tex]Mg[/tex] = 9.72 grams

So,

Total mass of [tex]2MgO[/tex] = Mass of [tex]2Mg[/tex] + Mass of [tex]O_2[/tex]

[tex]2\times 16.12g=2\times 9.72g+\text{Mass of }O_2[/tex]

[tex]\text{Mass of }O_2=32.24g-19.44g=12.8g[/tex]

Therefore, the total mass of oxygen gas released in the reaction will be, 12.8 grams