How does stoichiometry support the law of conservation of mass?

Stoichiometry is a concept based on balanced chemical equation and stoichiometry can support the law of conservation of mass.

We’ve discovered that in balanced chemical equation, the mass of reactants and products remain the same. 

What is law of conservation of mass? 

Law of conservation of mass is otherwise called the law of conservation of matter and it states that matter cannot be created nor destroyed 8but can be transformed from one form to another. 

So, it implies that in every balanced chemical equation, the mass of reactants and products remains the same (or equal) 

Recall that we emphasized earlier that stoichiometry is based on the concept of calculations involving quantities of reactants and products from balanced chemical equation. 

Since law of conservation of mass deals with mass of reactants before reaction equaling mass of products after reaction and this is simply illustrated by a balanced chemical equation. 

A balanced chemical equation is the basis and foundation of stoichiometry. 

So, when we ask how stoichiometry support law of conservation of mass does, we are trying to 

find out the relationship between stoichiometry and law of conservation of mass. 

I will prove how stoichiometry supports law of conservation of mass via two ways 

a. By experiment 

b. By theoretical approach 

1. By experiment 

We can prove how stoichiometry supports the law of conservation of mass using a simple experiment. 

From the experimental set up, you’ll notice that the mass of the reactants before reaction equals the mass of products after reaction 

This is verified by the weight (mass) shown by the weighing balance. 

So, since the mass (quantity of matter) of the reactants and products do not change, the law of 

conservation of matter or mass is verified. 

Second example is having like 40.6 grams of iron and Sulphur to still form 40.6 grams of iron II sulphide.

Fe + S === FeS

From this experiment, the mass of reactants before reaction started was weighed and we got 40.6 grams. After the reaction, the products formed were weighed and we got same mass. 

This proves that stoichiometry supports law of conservation of mass since mass (or matter)  remained the same but only was transformed from one from one form to another..

 

How do you verify the law of conservation of mass using stoichiometry? 

As I said earlier, law of conservation of mass can be illustrated theoretically. 

Example 1 

Check if the equation verifies the law of conservation of mass 

H₂ + Cl₂==2HCl 

Solution 

I will theoretically calculate the mass of the reactants and products. 

Reactants 

H₂= 1 x2 = 2 g 

Cl₂ = 35.5 X 2= 71 g 

Total = 73 grams 

Products 

36.5 x2 = 73 grams 

So theoretically we have same mass of reactants and products. 

Example 2 

Verify that this equation supports law of conservation of matter 

Mg + 2HCl == MgCl₂ + H₂ 

Solution 

For reactants 

Mg 

24g 

2HCl 

2 (1 +35.5) = 73 g 

Total 

24 + 73 = 97 grams 

For Products 

MgCl₂ 

24 +35.5 ×2 = 24 + 71 =95 grams 

H₂ 

1x 2 = 2 grams 

Total 

97 grams 

So we you compare the two masses, they are the same and thus the law of conservation of matter is 

verified 

Example 3 

 Show that the equation verifies the law of conservation of mass 

2Na + 2H₂O === 2NaOH + H₂ 

Solution  

For reactants 

Na 

2 x 23 = 46 g 

2H₂O 

2 (1 x 2+16) = 2 (18) = 36 g 

Total = 82 grams of the reactants 

For Products 

2NaOH 

2(23+16+1) = 2 x 40 = 80 g 

H₂ 

1 x 2 = 2 g 

Mass of products = 82 g 

The law is thus verified by having same mass of reactants and products 

Example 4 

Verify if the decomposition of calcium carbonate supports the law of conservation of matter. 

CaCO₃ === CaO + CO₂ 

_Solution  

_Reactants  

^CaCO₃ 

_{40+ 12+ 16x 3 = 100g}  

_Products  

_CaO  

_{40+ 16 = 56 g} 

CO₂ 

12 + 16 x 2 = 12 +32 = 44 grams 

Total = 56 g + 44 g = 100 g 

Example 5 

Finally let’s show how the formation of ammonia could be used to verify the law of conservation of matter. 

N₂+ 3H₂ ===2NH₃ 

Solution  

Reactants  

N₂ and 3H₂ 

N₂ = 14x 2= 28 g  

3H₂ = 3(1 x 2) = 6 g 

Total = 34 grams of the reactants 

Products  

2NH₃= 2 (14 + 1 x 3) = 2 (17) = 34 grams of the products 

All these examples prove how stoichiometry support law of conservation of matter