Laws of chemical combination inrtoduction
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There are basically two laws of chemical combination - Law of conservation of mass and Law of constant proportion.
The law of conservation of mass states that the mass of a closed system will remain constant in a chemical reaction. In other words, mass can neither be created nor destroyed in a chemical reaction. This law was first formulated by Antoine Laurent Lavoisier in 1789.
For example, 100 g of mercuric oxide, when heated in a closed test tube, decomposes to produce 92.6 g of mercury and 7.4 g of oxygen gas.
2 HgO (s) → 2Hg (l) + O2 (g)
Total mass of the reactant = 100 g
Total mass of the products = 92.6 + 7.4 g = 100 g
Hence, during the decomposition reaction, matter is neither created nor destroyed. Here, matter is made up of tiny mercuric (Hg) and oxygen (O) atoms. The given reaction shows that atoms can neither be created nor destroyed in chemical reactions.
According to the law of constant proportion, a chemical substance always contains the same elements in a fixed proportion by mass, irrespective of its source. The law of constant proportion is also known as the law of definite proportion. This law, which was introduced by Proust, stated that ‘in a compound, the elements are always present in definite proportions by mass’.
For example, pure water obtained from any source (well, river, lake, or sea) and from any country (India, Russia, America, etc.) will always contain two hydrogen atoms and one oxygen atom. Hydrogen and oxygen respectively combine together in the ratio of 1:8 by mass to form water. The ratio by the number of atoms for water will always be H : O = 2 : 1. Thus, 18 g of water contains 2 g of hydrogen and 16 g of oxygen.Similarly, in ammonia, nitrogen makes up 14/17 of the mass of ammonia while hydrogen makes up the remaining 3/17 of the mass. Irrespective of the source from which ammonia is obtained, it will always contain nitrogen and hydrogen in the ratio of 14: 3 by mass. Thus, 17 g of ammonia contains 14 g of nitrogen and 3 g of hydrogen, and 34 g of ammonia contains 28 g of nitrogen and 6 g of hydrogen.
The law of conservation of mass states that the mass of a closed system will remain constant in a chemical reaction. In other words, mass can neither be created nor destroyed in a chemical reaction. This law was first formulated by Antoine Laurent Lavoisier in 1789.
For example, 100 g of mercuric oxide, when heated in a closed test tube, decomposes to produce 92.6 g of mercury and 7.4 g of oxygen gas.
2 HgO (s) → 2Hg (l) + O2 (g)
Total mass of the reactant = 100 g
Total mass of the products = 92.6 + 7.4 g = 100 g
Hence, during the decomposition reaction, matter is neither created nor destroyed. Here, matter is made up of tiny mercuric (Hg) and oxygen (O) atoms. The given reaction shows that atoms can neither be created nor destroyed in chemical reactions.
According to the law of constant proportion, a chemical substance always contains the same elements in a fixed proportion by mass, irrespective of its source. The law of constant proportion is also known as the law of definite proportion. This law, which was introduced by Proust, stated that ‘in a compound, the elements are always present in definite proportions by mass’.
For example, pure water obtained from any source (well, river, lake, or sea) and from any country (India, Russia, America, etc.) will always contain two hydrogen atoms and one oxygen atom. Hydrogen and oxygen respectively combine together in the ratio of 1:8 by mass to form water. The ratio by the number of atoms for water will always be H : O = 2 : 1. Thus, 18 g of water contains 2 g of hydrogen and 16 g of oxygen.Similarly, in ammonia, nitrogen makes up 14/17 of the mass of ammonia while hydrogen makes up the remaining 3/17 of the mass. Irrespective of the source from which ammonia is obtained, it will always contain nitrogen and hydrogen in the ratio of 14: 3 by mass. Thus, 17 g of ammonia contains 14 g of nitrogen and 3 g of hydrogen, and 34 g of ammonia contains 28 g of nitrogen and 6 g of hydrogen.
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