What are Laws of Chemical Combinations?

Laws governing the combination of elements to form compounds are called Laws of Chemical Combination. Law of Conservation of Mass, Law of Definite Proportions, Law of Multiple Proportions, Gay Lussac’s Law of Gaseous Volumes, Avogadro’s Law are Laws of Chemical Combination in the Chemistry.

Let’s discuss each of the these Chemical Combinations laws one-by-one.

Law of Conservation of Mass

Law of Conservation of Mass was put forth by Antoine Lavoisier in 1789 after doing some experimental studies. In all of the experimental studies which Lavoisier did, he observed that during combustion reactions there is no net change of mass, meaning mass before reaction remains same as mass after reaction. From these experiments, he concluded that Mass Can Neither Be Created Nor Be Destroyed. Antoine called this ‘Law of Conservation of Mass’.

Examples of Law of Conservation of Mass

  1. Mixing together two liquids – If 5, 10 grams of two liquids A, B are mixed together then final mass of solution will be 15 gram as per Law of Conservation of Mass.
  2. Burning Carbohydrates(like Fossil Fuels) – If 30 grams of Petrol is burned then equivalent amount of gases would be produced as per Law of Conservation of Mass.

Law of Definite Proportions

Law of Definite Proportions state was put forwards by French Chemist named Joseph Proust. From different observations, Joseph concluded that “A Given Compound Always Contains Exactly The Same Proportion Of Elements By Weight“. This means that any compound no matter whatever source it is extracted from will always be containing same proportion of elements. For example – Water(H2O) no matter whether from underground or from sea will always be containing Hydogen and Oxygen in proportion as 2 : 1.

Law of Multiple Proportions

Law of Multiple Proportions was proposed by John Dalton(He’s also known as The Father of Chemistry) in 1803. According to this law – “If two elements can combine to form more than one compound, then masses of one element that combine with a fixed mass of the other element, are in the ration of small whole numbers.
Below I’ve explained this law using an example.

Example of Law of Multiple Proportions

Hydrogen and Oxygen can combine to form either water(H2O) or hydrogen peroxide(H2O2). Below are reactions leading to formation of Water and Hydrogen Peroxide.

    \[2 \mathrm{H}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}\]

    \[ \mathrm{H}_{2}+\mathrm{O}_{2} \rightarrow  \mathrm{H}_{2} \mathrm{O}\]

In both of the above reactions, masses of oxygen(32g) which combined with masses of hydrogen is 2 : 1 which is a simple whole number ratio.

Gay Lussac’s Law of Gaseous Volumes

Gay Lussac’s Law of Gaseous Volumes also known as Law of Gaseous Volumes was first proposed by Gay Lussac in 1808. This law states that “When gases combine or are produced in a chemical reaction they do so in a simple ratio by volume, provided all gases are at the same temperature and pressure.

    \[2 \mathrm{H}_{2}+\mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}\]

In the above reaction, 100mL of hydrogen and 50mL of oxygen combines with each other in ratio as 2 : 1 producing water.

Avogadro’s Law

In 1811, Lorenzo Romano Amedeo Carlo Avogadro known as just Avogadro proposed that “Equal volumes of all gases at the same temperature and pressure should contain equal number of molecules.” At the time when Avogadro proposed this distinction between – Atom and Molecule was not clear.

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