Laws of Chemical Combination for Elements and Compounds

Chemistry is the study of matter, composition of matter and its different forms. Matter changes into different forms by chemical combinations. These chemical combinations of different elements and compounds follow a set of laws. This is the reason why we always balance chemical equations. 

Here we are providing you five basic laws of chemical combination which rule the chemical combinations of elements- 

1. Law of Conservation of Mass – 

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Law of conservation of mass states that “matter can neither be created nor destroyed in a chemical reaction.”

It was given by French Chemist, Antoine Lavoisier in 1789. Mass of reactants and mass of products will always be equal in a chemical reaction. As according to this law mass can neither be created nor destroyed. This is the reason why we always balance a chemical equation. 

Thus, for any chemical reaction or chemical change the mass of the reactants is equal to the mass of product formed. This law can be explained by Dalton’s atomic theory. According to Dalton’s atomic theory –Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction. 

Example - Formation of water – 

2H2 + O2 🡪 2H2O 

Mass of reactants = 4 + 32 = 36g

Mass of products = 2(2+16) = 2(18) = 36g

As we can see mass of reactants and mass of product is equal in the reaction. So, it proves the law of conservation of mass. 


2. Law of Definite Proportions 

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a law of definite proportions was proposed by Joseph Proust in 1799. It is also known as law of constant proportions. According to this law in a chemical substance the elements are always present in definite proportions by mass. John Dalton’s theory provided an explanation for the law of constant proportions as well. As according to John Dalton’s theory, the relative number and kinds of atoms are constant in a given compound. This statement supports the law of constant proportions. 

Example - In a water molecule the ratio of mass of  hydrogen and mass of oxygen always remains the same which is 1:8. You can take water molecules from any source but hydrogen and oxygen will always remain in 1:8 ratio by mass in a water molecule. 


3. Law of Multiple proportions 

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Law of multiple proportions was given by John Dalton in 1804. According to this law if elements combine to form two or more than two different kinds of compounds, then the masses of these elements in the compounds are in the ratio of small whole numbers. Dalton’s atomic theory states that atoms combine in the ratio of small whole numbers to form compounds. 

Example – Carbon forms two oxides with oxygen- Carbon monoxide (CO) and carbon dioxide (CO2). In these compounds (one molecule) mass of carbon is 12g (fixed) and the ratio of masses of oxygen in both compounds CO and CO2 is 16:32 or 1:2. 


4. Gay Lussac’s Law of Gaseous Volumes 

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Law of Gaseous Volumes was proposed by Joseph Louis Gay-Lussac in 1808. According to this law when measured at the same temperature and pressure, the ratio of the volumes of reacting gases are small whole numbers. This can be considered as a different form of law of definite proportions. As this law is with respect to volume while law of definite proportion is with respect to mass. 

Example - 

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5. Avogadro’s Law 

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Avogadro’s law was given by Amedeo Avogadro in 1811. According to this law equal volumes at the same temperature and pressure contain equal numbers of moles of gases. It means that 2 litres of oxygen and 2 litres of nitrogen will contain the same numbers of moles if measured at same temperature and pressure. 

Above we have discussed the law of chemical combination in a simple manner, if still you have doubts and want more detailed notes on the topic then register yourself on Vedantu and get the access of free PDFs of NCERT Solutions, study material etc.