According to the law of conservation of mass (or the law of conservation of matter), matter is neither created nor destroyed in a chemical reaction or change. It means the total mass of products is equal to the total mass of reactants in the chemical reaction. In 1774, scientist Antoine Lavoisier given this law.
The substances which react (or take part) in a chemical change are called reactants. Whereas, the new substances formed (or produced) as a result of chemical change are called products. The law of conservation of mass or matter says that the total mass of products is equal to the total mass of reactants in a chemical reaction. Hence, there is no change in the mass during the chemical change.
Since there is no gain or loss in mass in a chemical reaction, therefore, the mass of matter remains conserved (i.e. same). Let’s understand this with the help of a general example.
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Assume that we carry out a chemical reaction between reactants A and B to produce products C and D. Then,
A + B → C + D
Mass of reactants (A + B) = Mass of products (C + D)
Or, mass of reactants = mass of products
Law of Conservation of Mass or Matter Example
According to the law of conservation of mass (or matter), there is no increase or decease in the total mass of matter during a chemical or physical change. This law will be more clear with the help of the following examples.
Example 1: When we heat calcium carbonate, a chemical reaction occurs to form calcium oxide and carbon dioxide. We can experiment it if 100 grams of calcium carbonate decomposes completely, 56 grams of calcium oxide and 44 grams of carbon dioxide will form. Look at the reaction below.
In this example, calcium carbonate is a reactant whose mass is 100 grams. Calcium oxide and carbon dioxide are the products whose total mass is 56 grams + 44 grams = 100 grams. As you can see, the total mass of products is equal to the total mass of the reactant and there is no change in the mass or matter during the chemical reaction. The mass of matter remains conserved (or the same). Thus, this example supports the law of conservation of mass or matter.
Example 2: Suppose we take a piece of ice (solid water) in a small conical flask. We cork the flask tightly and measure its weight. Now we will heat the flask gently to melt the ice (solid) into water (liquid). Again, we will measure its weight. We will find that there is no change in the weight when the physical change takes place. This example proves the law of conservation of mass or matter.
Example 3: When we burn a sample of metallic magnesium in the presence of oxygen (i.e. air) the magnesium reacts or combines with oxygen to form magnesium oxide that is a white powder. Here, magnesium and oxygen are the reactants and magnesium oxide is the product. This chemical reaction produces a large amount of heat energy and light energy. When we measure the weight of the product, magnesium oxide, we will find that it will be heavier than the original piece of magnesium.
This increase in the mass of solid is due to the reaction of oxygen with magnesium to form magnesium oxide. Now if we perform the same experiment in a closed container, we will find that the mass of product, magnesium oxide, is equal to the sum of masses of reactants (magnesium and oxygen) that reacted to form it. Similar statements are applicable for all the chemical reactions.
Importance of Law of Conservation of Matter
The law of conservation of mass is important to us because of the following reasons. They are as:
- This law helps to write the correct chemical formulae and equations.
- This conservation law helps to know the weights of chemicals requisite to obtain a specific quantity of the product (or products) in the chemical reaction or change. Such calculations restrain the wastage of chemicals, especially in the manufacture of chemicals.
Example Problem based on Law of Conservation of Mass
Example 1: In an experiment, 4.90 g of KClO3 is heated to produce 1.92 g of oxygen and 2.96 g of KCl that residue left. Prove that this data verifies the law of conservation of matter or mass.
Solution:
Mass of KClO3 taken = 4.90 grams
Total mass of the products (KCl + O2) = 2.96 + 1.92 = 4.88 grams
Difference between the mass of reactant and total mass of products = 4.90 – 4.88 = 0.02 g. This very small difference may occur because of experimental errors. Thus, this data verified the law of conservation of mass.
Example 2: In an experiment, 5.3 g of sodium carbonate (Na2CO3) combined (or reacted) with 6 g of ethanoic acid (CH3COOH) to produce 8.2 g of sodium ethanoate (C2H3NaO2) , 2.2 g of carbon dioxide (CO2), and 0.9 g of water (H2O). Prove that this data verifies the law of conservation of mass.
Solution:
From the above experiment, it is clear that sodium carbonate and ethanoic acid are the reactants, while sodium ethanoate, carbon dioxide, and water are the products. In this problem, we will calculate the total mass of reactants and products separately. Then, we will compare of both results. If both are equals, the law of conservation of mass gets verified.
Total mass of reactants = mass of sodium carbonate + mass of ethanoic acid = 5.3 + 6 = 11.3 g
Total mass of products = mass of sodium ethanoate + mass of carbon dioxide + mass of water = 8.2 + 2.2 + 0.9 = 11.3 g
From the above calculation, we have found that the total mass of reactants is equal to total mass of the products which verified the law of conservation of mass.
Example 3: When we heat calcium carbonate (CaCO3), it decomposes into calcium oxide (CaO) and carbon dioxide (CO2). When 10 g of calcium carbonate is decomposed completely, 5.6 g of calcium oxide is produced. Calculate the mass of carbon dioxide produced in the chemical reaction.
Solution:
From the above example, it is clear that calcium carbonate is the reactant while calcium oxide and carbon dioxide are the products.
According to the law of conservation of mass,
mass of reactants = mass of products
Mass of calcium carbonate = Mass of calcium oxide + Mass of carbon dioxide
Mass of carbon dioxide = Mass of calcium carbonate – Mass of calcium oxide
Mass of carbon dioxide = 10 g – 5.6 g = 4.4 g (Ans.)
In this tutorial, we have explained the law of conservation of mass or matter with the help of some important examples. Hope that you will have understood the basic points of this law and enjoyed it.
Thanks for reading!!!
