The law of conversation of mass may be demonstrated by the union of hydrogen (H2) and oxygen (O2) to form water. If the H2 and O2 are weighted before they unite it will be found their combined weight is equal to the weight of water (H2O) formed.
Chemistry deals with the matter and the changes occurring in it, chemists are particularly interested in these changes, where one or more substances are changed in to quite different substances. They had found that these chemical changes are governed by some empirical laws known as laws of chemical combinations.
These laws are:
1. Law of conservation of mass.
2. Law of constant composition (or) Law of definite proportions
3. Law of multiple proportions
4. Law of reciprocal proportions.
Matter under goes changes. However, it has been found that in all chemical changes, there is no change in the mass of the substances being changed. For example, in iron (Fe) increase in weight on rusting in because of its combination with oxygen from the air and the increase in weight is exactly equal to the weight of oxygen combined. The French chemist Lavosier, (1785) tired to learn about chemical changes by weighing the quantities of substances used in chemical reaction. He found that when a chemical reaction was carried out in a closed system, the total weight of the system was not changed. The most important reaction that Lavosier performed was the decomposition of the red oxide of mercury to from metallic mercury and and a gas, he named this gas as oxygen. Lavosier summarised his finding by formulating a law, which is known as law of conversation mass. It states that mass is neither created nor destroyed during a reaction. In other words, in any chemical reaction the initial weight of reacting substances is equal to the final weight of the products.
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