Law Of Conservation Of Mass: Definition, History, 2 Examples + VIDEO

Like other pure sciences, chemistry also knows several kinds of laws. One of them is the Law Of Conservation Of Mass (Lavoisier Law) of Chemical Science.

This one law can be seen in daily life close to us. For example, an object whose shape changes and a reaction occurs to it. For example, rusting iron or burning wood. Then the wood or iron was weighing and it was found that there was a change in weight.

Both iron and wood feel lighter after a change of shape. Surely we would have thought that the mass of things had changed. However, it turns out that the assumption was refuted by French scientists. Through his discovery, he explained that the material of an object has been always the same, even though it has been used in various processes that affect its shape.

To understand it more deeply, please see the explanation below.

Law Of Conservation Of Mass Definition

The law of conservation of mass or often referred to as Lavoisier law is a law that states that reactions involving the transfer of matter and energy to a closed system, the mass of the system will remain constant (unchanged).

The mass quantity cannot change if it is not added or released intentionally. Thus, the mass is eternal. This law states that mass cannot be created or destroyed, just like energy. Lavoisier’s law covers all chemical reactions, nuclear reactions, and decay reactions on closed (isolated) systems.

Law Of Conservation Of Mass History

Antonie Lavoisier (1743–1794) was a pioneer who believed in the importance of making quantitative observations in experiments, trying to heat 530 grams of metal mercury in an air-connected container in a measuring cylinder on a closed system. It turns out that the volume of air in the cylinder is reduced by 1/5 part.

The mercury turns into 572.4 grams of mercury oxide. The amount of mercury mass increase by 42.4 grams is equal to 1/5 of the lost air part that is oxygen.

Law Of Conservation Of Mass Statement

Mercury + Oxygen Gas → Mercury Oxide

530 grams + 42.4 grams –> 572.4 grams

Based on the above experiment Lavoisier formulated the Law of Mass Eternity which reads:

In a chemical reaction the total mass of all the substances taking part in the reaction remains the same.

Law Of Conservation Of Mass Example

Magnesium combustion reaction

In a magnesium combustion with oxygen, a sum of 30 grams of magnesium precisely reacts with 20 grams of oxygen, then in that reaction will be produced (30+20) grams = 50 grams of magnesium oxide compounds.

If in other conditions reacted between 35 grams of magnesium and 20 grams of oxygen, it turns out that at the end of the reaction, magnesium oxide produced 50 grams, and still remaining 5 grams of magnesium. In this case it remains the law of Lavoisier because the mass before the reaction (35+20) grams and the mass after the reaction (50+5) grams. But the explanation for, why not all magnesium reacts with oxygen is related to another chemical law that is Proust law.

Reaction to burning wood

The result of burning wood is ash. The mass of ash as a mass of reactive substances will be lighter than the mass of wood as a substance after the reaction. This condition occurs because there is a reactive result other than ash leaving the system. The result of the reaction that left the system in the form of carbon dioxide, smoke, and water vapor.

If all substances before and after the reaction are weighed then the wood mass equation + oxygen period = ash period + carbon oxide mass + water vapor mass + smoke mass.

Read also:
Atom Definitions, and The Origin of Atomic Theory

Examples of the Law Of Conservation Of Mass in daily life also occur in burning candles.