State the Law of Conservation of Mass.

Short Answer

The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction. This means the total mass of the reactants before a reaction is always equal to the total mass of the products formed after the reaction. Matter simply changes its form but the total amount remains the same.

This law helps us understand that during any chemical process, atoms are rearranged but not created or lost. It is an important principle in chemistry used in balancing equations and studying chemical reactions. The law was first stated by Antoine Lavoisier.

Detailed Explanation :

Law of Conservation of Mass

The Law of Conservation of Mass is one of the most important principles in chemistry. It explains how mass behaves during chemical reactions and physical changes. According to this law, mass can neither be created nor destroyed, meaning the total mass remains constant throughout a reaction. Only the arrangement of particles changes, but their total quantity stays the same. This principle is the foundation for understanding chemical equations, balancing reactions, and studying the movement of atoms during chemical processes.

The law was introduced by the French scientist Antoine Lavoisier in the late 18th century. His experiments showed that even when substances appear to disappear—such as when a metal burns or ice melts—their total mass remains unchanged if measured carefully.

Meaning of the Law

The law states:
“In any chemical reaction, the total mass of the reactants is equal to the total mass of the products.”

This means that:

  • No new mass is created during the reaction
  • No mass is lost during the reaction
  • Atoms rearrange to form new substances, but their total number stays the same
  • The total mass before and after the reaction must be equal

For example, when hydrogen reacts with oxygen to form water, the number of atoms remains the same, even though the substance formed is different. So, the mass is conserved.

Why Mass is Conserved

Matter is made up of atoms, and atoms are extremely small particles that cannot be created or destroyed in a chemical reaction. They only rearrange to form new compounds. Since the number of atoms is the same before and after the reaction, the mass also remains unchanged.

For example:

  • In burning magnesium, magnesium combines with oxygen to form magnesium oxide.
  • Even though the appearance changes, the total mass of magnesium and oxygen equals the mass of magnesium oxide formed.

This proves that mass is conserved.

Examples Demonstrating Conservation of Mass

Example 1: Burning of Carbon
Carbon reacts with oxygen to form carbon dioxide.
If 12 g of carbon reacts with 32 g of oxygen, the total mass of carbon dioxide produced will be:
12 g + 32 g = 44 g
Mass before = Mass after

Example 2: Dissolving Salt in Water
If 10 g of salt is dissolved in 100 g of water, the total mass of the solution becomes:
10 g + 100 g = 110 g
No mass is lost; it only changes form.

Example 3: Formation of Water
Hydrogen gas reacts with oxygen gas to form water.
Mass of hydrogen + mass of oxygen = mass of water
Even though gases combine to form a liquid, the mass remains the same.

Importance of the Law in Chemistry

This law is very important because it helps us:

  • Balance chemical equations – every equation must follow this law
  • Predict amounts of products formed
  • Understand reactions happening in closed containers
  • Study stoichiometry, which deals with mass relationships in reactions
  • Conduct experiments accurately, as mass must remain constant

The law is used in labs, industries, pharmaceuticals, environmental studies, and chemical analysis.

Role in Balancing Chemical Equations

When writing chemical equations, the number of atoms of each element must be the same on both sides. This is because atoms cannot be created or destroyed. Balancing equations follows the Law of Conservation of Mass.

For example:
H₂ + O₂ → H₂O (Unbalanced)
Balanced form: 2H₂ + O₂ → 2H₂O
Here the number of hydrogen and oxygen atoms are equal on both sides.

Physical Changes and Conservation of Mass

This law also applies to physical changes such as melting, boiling, freezing, and dissolving. For instance, when ice melts to form water, the mass of water obtained is equal to the mass of ice taken.

Conclusion

The Law of Conservation of Mass states that mass can neither be created nor destroyed during a chemical reaction. The total mass of reactants is always equal to the total mass of the products. This law forms the basis of chemical equations and helps us understand how atoms rearrange during reactions. Introduced by Lavoisier, it remains one of the fundamental principles in chemistry.