Atoms and Molecules

Introduction and Laws of Chemical Combination

Have you seen rust forming over metals? Isn’t it just so hard to remove? But on the first note how does it occur? Well, rust occurs because of chemical combination. But what is a chemical combination? Let us find out!

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What do you understand by chemical combination? A combination reaction, termed as synthesis reaction, happens when two or more reactants or constituents, combine to form a new product. Do remember that the resultant product would always be a compound. In chemistry, there are four prime laws which are abided faithfully.

Laws of Chemistry

While gaining knowledge about chemistry, one must patiently understand four principal laws that govern the process by which atoms combine. These laws are mentioned below:

  • The law of the Conservation of Mass
  • Law of Constant Proportions
  • The law of Multiple Proportions
  • Law of Reciprocal Proportions

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Law of the Conservation of Mass

Considering chemical reactions, pure combinations of different elements termed as compounds do get rearranged. Supposedly, in nuclear reactions, the nucleus of atoms modify. Looking at both cases, mass is preserved while new substances are created. Let’s try to understand this through a chemical as well as nuclear reaction. You’ll see how mass before and after a reaction stays similar.

Solid calcium reacting With Hydrobromic Acid

Ca + HBr → CaBr2 + H2

One can notice here that, there is single bromine and hydrogen present on the left side, whereas there are two atoms for each element available on the product side. However, this is impractical since one hydrogen atom and bromine can’t be produced out of anywhere. In order to show what actually happens there is a need to balance the equation along with coefficients.

Ca + 2HBr → CaBr2 + H2

Do note that, the coefficient placed in front of HBr tends to make the equation stable or balanced for mass.

Law of Constant Proportions

As per the law of constant proportions, the same type of compounds will always hold the same ratio of elements. For example, carbon dioxide will always hold the ratio of 1 carbon atom to two atoms of oxygen leading to the formula CO2. Furthermore, the ratio of mass also stays constant. This law was framed and demonstrated by Joseph Louis Proust in the year 1799.

Law of Multiple Proportions

When two elements lead to the creation of two or more compounds, the ratio of the masses associated to the second element in every compound can be denoted as small whole numbers. This is the law of multiple proportions which was formulated by John Dalton. You can notice it to be a combination of other laws.

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Law of Reciprocal Proportions

Chemical combination and its resultants are very well elaborated and justified with the above mentioned three laws. The final law termed as the law of reciprocal proportions focuses on the combination of two different elements combining with a similar quantity of the third element. If this happens, the ratio at which the combination will occur stays the same or a multiple of the definite proportion in which they combine. The law was suggested by Jeremias Ritcher in the year 1792.

Questions For You

Q. Carbon combines with oxygen to result in two different compounds (based on different circumstances). One is the common gas CO2, while the other one is CO. Can you tell if they abide the law of multiple proportions?

Ans: The answer to this is YES. The law of multiple proportions is justified and we’ll see how. Mass of carbon is 12 u and oxygen has a mass of 16 u. Hence, we can say that 12g of carbon mixed or combined with 32g of oxygen resulting in CO2. Likewise, 12 g of carbon merges with 16 g of oxygen to create CO.

Therefore, the ratio of oxygen considering the first and second compound tends to be: 2:1 = 32/16 = 2 (a whole number).

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