Law of Reciprocal Proportions

The law of reciprocal proportions, sometimes known as the law of equivalent proportions or permanent ratios, is another name for the rule of reciprocal proportions. It is one of the basic rules of stoichiometry, along with definite and many proportions laws. Jeremias Richter, a German scientist, introduced the statute in 1791. This is comparable to the multiple proportions law.

History of Law of Reciprocal Proportions

Richter introduced the concept of reciprocal proportions in essence after determining the neutralisation ratios of metals with acids.

When two elements, A and B, have an affinity for two others, C and D, the ratio of the quantities C and D that saturate the same amount of A are the same as the ratio of the quantities C and D that saturate the same amount of B, according to Berzelius in the early nineteenth century. Later, Jean Stas demonstrated that the stoichiometric rules were true within experimental error.

Law of Reciprocal Proportions Definition

“When two elements combine independently with a fixed mass of the third element, the ratio of their masses in which they do so is either the same or some whole number multiple of the ratio they mix,” stated Ritcher.

The simple whole-number ratio is established only when the masses of the combining elements are merged in proportion to their equal weight. As a result, the law of reciprocal proportion is also known as the law of equal proportion.

CO2, SO2, and CS2 are examples of carbon, sulphur, and oxygen compounds. In CO2, there are 12 parts by mass of carbon and 32 parts by bulk of oxygen, but in SO2, there are 32 parts by mass of sulphur and 32 parts by mass of oxygen. 12:32 or 3:8 is the mass ratio of carbon and sulphur when combined with a fixed quantity of oxygen.

12 parts carbon by mass mix with 64 parts sulphur by mass, resulting in a ratio of 12:64, or 3:16.

As a result, the proportions are 2:1.

All preceding principles governing the relative weights of components required to produce compounds apply only to compounds with a defined formula. While most molecules have a set formula, some may have an indeterminate formula. Non-stoichiometric compounds have a composition that varies depending on the preparation circumstances.

The Law of Reciprocal Proportions’ Limitations:

The presence of the element’s isotopes generates differences comparable to those seen in the law of constant proportions. As a result, the same isotope or combination of isotopes should be employed during the synthesis of a series of compounds.

Because there are a limited number of components that will mix with the third element and also with one another, as a result, the law only applies to a small number of items that display the feature in question.

Based on Dalton’s Atomic Theory, an explanation of the Law of Reciprocal Proportion Definition:

According to Dalton’s atomic theory, all atoms of the same element are identical, and compounds are generated by combining atoms of various elements in a simple ratio of whole numbers. As a result, when the weights of the components are combined with a fixed weight of another element, the weights of the elements should have a simple ratio to the weights of the elements when they combine. This clarifies the reciprocal proportion rule.

The Law of Combining Volumes of Gay Lussac

When two gases react, the volumes of the reacting gases and the products have a simple whole-number ratio, as long as all the volumes are measured at the same temperature and pressure.

Step 1: Hydrogen and oxygen combine to make water.

Step 2: H2 + 12O2 = H2O

Step 3: 2H2(g) + O2(g) = 2H20(g) (Balanced Equation)

Water vapour is formed when two volumes of hydrogen react with one volume of oxygen. i.e., gases have a volume ratio of 2:1:2, a simple whole number ratio.

Example of Law of reciprocal proportion

1st Example:

Consider the following three substances: methane, carbon dioxide, and water.

Methane and carbon dioxide are formed when hydrogen and oxygen react with carbon independently. When various weights of hydrogen (4) and oxygen (32) combine with a given weight of carbon (12), the ratio is 4:32, or 1:8. Now hydrogen and oxygen unite to make water (H20), with a weight ratio of 2:16 (or 1:8) for hydrogen and oxygen. This ratio is the same as the one obtained before. As a result, the reciprocal proportion law is shown.

2nd Example:

Phosphorus trihydride, phosphorus trichloride, and hydrogen chloride are three chemicals to consider.

Phosphorus trihydride and phosphorous trichloride are formed when hydrogen and chlorine react with phosphorus independently. The phosphorus’s(31) set weight is combined with a ratio of varying weights of hydrogen (3) and chlorine (106.5). 1:35.5, i.e. 1:35.5

Now hydrogen and chlorine mix to make hydrogen chloride, with a weight ratio of 1:35.5 for hydrogen and chlorine. This ratio is the same as the one obtained before. As a result, the reciprocal proportion law is shown.

Conclusion

The law’s approval allowed for creating tables of element equivalent weights. Chemists commonly employed these comparable weights in the nineteenth century. The law of definite proportions and the law of many proportions are two further stoichiometric laws. The set composition of each compound created between elements A and B is referred to as the law of definite proportions. The stoichiometric connection between two or more distinct compounds generated by elements A and B is described by the law of multiple proportions.