Laws Of Chemical Combination For Elements And Compounds
Chemistry is the study of the transformation of matter from one form to the other. These transformations often occur as a result of the combination of two different types of matter. The combination of different elements to form compounds is governed by certain basic rules. These rules are referred to as laws of chemical combination. There are five basic laws of chemical combination that govern the chemical combinations of elements:
1. Law of Conservation of Mass
In simple terms, this law states that matter can neither be created nor destroyed. In other words, the total mass, that is, the sum of the mass of reacting mixture and the products formed remains constant. Antoine Lavoisier gave this law in the year 1789 based on the data he obtained after carefully studying numerous combustion reactions.
2. Law of Definite Proportions
Joseph Proust, a French chemist stated that the proportion of elements by weight in a given compound will always remain exactly the same. In simple terms, we can say that irrespective of its source, origin or its quantity, the per cent composition of elements by weight in a given compound will always remain the same.
3. Law of Multiple Proportions
This law states that if two elements combine to form more than one compound, the masses of these elements in the reaction are in the ratio of small whole numbers. This law was given by Dalton in the year 1803.
4. Gay Lussac’s Law of Gaseous Volumes
In 1808, Gay Lussac gave this law based on his observations. This law states that when gases are produced or combine in a chemical reaction, they do so in a simple ratio by volume given that all the gases are at the same temperature and pressure. This law can be considered as another form of the law of definite proportions. The only difference between these two laws of chemical combination is that Gay Lussac’s Law is stated with respect to volume while the law of definite proportions is stated with respect to mass.
5. Avogadro’s Law
Avogadro proposed this law in the year 1811. It stated that under the same conditions of temperature and pressure, an equal volume of all the gases contains an equal number of molecules. This implies that 2 litres of hydrogen will have the same number of molecules as 2 litres of oxygen given that both the gases are at the same temperature and pressure.
Laws of chemical combination
Chemistry usually involves chemical reactions where two or more elements combine to produce a single compound. The reactions involving the combination of various elements to produce a single compound are governed by the 5 laws of chemical combination. The five laws of chemical combination are:
- Law of conservation of mass
- Law of definite proportions
- Law of multiple proportions
- Gay Lussac’s law of gaseous volumes
- Avagadro’s law of chemical combination
Let us understand what these five laws have to say about various chemical combinations taking place in nature.
Law of conservation of mass
The law of conservation of mass was proposed by Antonie Lavoisier in 1789 and was based on results obtained from various combustion reactions.
According to the law of conservation of mass, “mass can neither be created nor destroyed, it can only be transformed from one form to another”.
In chemistry, the law of conservation of mass states that the total mass of the product obtained by chemical combination is equal to the sum of the mass of all reactants involved.
Example – The heating of calcium carbonate (10grams) produces calcium oxide (5.6 grams) and calcium dioxide (4.4 grams).
According to the law of conservation of mass,
Total mass of reactants = Total mass of products
Mass of calcium carbonate = Mass of calcium oxide + Mass of carbon dioxide
10.0 grams = 5.6 grams + 4.4 grams
10.0 grams = 10.0 grams
Law of definite proportions
Joseph Proust proposed the law of definite proportions in 1799. It is called Proust’s law or the law of constant proportions.
According to the law of definite proportions, elements are always combined in specific definite proportions only. It means that elements always combine in a specific ratio irrespective of the number of reactants taken or the source from which they were obtained.
Example – Ethyl alcohol (C2H5OH).
Irrespective of the total amount of ethyl alcohol present, its combination consists of 52% of carbon, 35% of oxygen, and 13% of hydrogen by weight. This is according to the law of constant proportions.
Law of multiple proportions
John Dalton proposed the law of multiple proportions in 1804.
According to the law of multiple proportions, Whenever the same two elements combine to form more than one compound, the various masses of an individual element that combine with the same mass of the other elements exist in the ratio of small whole numbers.
Example – Consider carbon and oxygen atoms. Carbon and oxygen atoms combine to give two different types of products – Carbon monoxide and carbon dioxide. In carbon monoxide, the amount of oxygen present for one carbon atom i.e. 12.0grams is 16.0 grams. In carbon dioxide, the amount of oxygen present for one carbon atom 12.0 grams is 32.0 grams. The ratio of the amount of carbon present in carbon monoxide to the amount of carbon present in carbon dioxide is 32:16 or 2:1.
- Gay Lussac’s Law of gaseous volumes
Gay Lussac’s proposed the law of gaseous volumes in 1808.
According to Gay Lussac’s law of gaseous volumes, the ratio of the volumes of all gaseous reactants and products can be represented in small whole numbers. When gases react at a particular pressure and temperature, the ratio of volumes of reactants and products can easily be expressed in small whole numbers.
Example – The combination of hydrogen gas and chlorine gas is governed by Gay Lussac’s law of gaseous volumes.
H2 + Cl2 → 2 HCl
In this example, one volume of Hydrogen gas combines with one volume of chlorine gas to produce 2 volumes of HCl gas. The ratio of the volume of hydrogen gas, chlorine gas, and HCl is 1:1:2.
- Avagadro’s law of chemical combination
Avagadro proposed the fifth law of chemical combination in 1811.
According to Avagadro’s law of chemical combination, at a given constant temperature and pressure, the volume of gaseous molecules is directly proportional to the total number of moles. Avogadro’s law is expressed as follows.
V ∝ n
Where V is the volume of gaseous molecules,
And n is the total number of moles of the gas.
V = k × n
Where k is the proportionality constant.
According to Avagadro’s law of chemical combination,
Where V1 is the volume and n1 is the number of moles of one gas. And V2 is the volume and n2 is the number of moles of another gas.
Example – Blowing of helium gas into a balloon. As the total number of moles of helium gas blown into the balloon increases, the overall volume of the balloon also increases.
Laws of Chemical Combination
When you write the various chemical equations, do you balance them? What happens when you don’t balance them? Your marks get cut. That is okay. But, what exactly happens? There are various laws of Chemical Combinations that govern these facts. So, apart from getting your marks cut, these laws are important because they help to keep things in place. What do we mean by this? Let us read about it below!
Chemistry is the study of the change of matter from one form to the other. These changes often occur as a result of the combination of two different types of matter. There are certain rules that govern the combination of different elements to form different compounds. These rules are, what we call, the laws of chemical combinations.
There are five basic laws of chemical combinations that govern the chemical combinations of elements. What are they and what do they signify? Let us read more about these laws in the section below.
1) Law of Conservation of Mass
French chemist, Antoine Lavoisier in 1789, studied this law. This law states that “In all physical and chemical changes, the total mass of the reactants is equal to that of the products” or “Mass can neither be created nor destroyed.”
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We also refer to this law as the law of indestructibility of matter. The mass and energy are interconvertible but the total sum of the mass and energy during any physical or chemical change remains constant. That is why your teacher cuts your marks when you don’t balance the equations! Understand now?
2) Law of Constant Composition or Definite Proportions
French chemist, J.L. Proust in 1799, discovered this law. It states that “A chemical compound is always found to be made up of the same elements combined together in the same fixed proportion by mass”.
For example, a sample of pure water from various sources or any country is always made up of only hydrogen and oxygen. These elements are always in the same fixed ratio of 1:8 by mass. We can prepare a sample of carbon dioxide in the laboratory. We can do this in various ways like:
- Heating limestone
- Burning coal in air
- The action of dilute hydrochloric acid on marble
- Heating sodium carbonate
However, we will always find that it contains the same elements, carbon, and oxygen, in the same fixed ratio of 3:8 by mass.
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Limitation of this Law
It is not applicable if an element exists in different isotopes which may be involved in the formation of the compound. The elements may combine in the same ratio but the compounds formed may be different.
3) Law of Multiple Proportions
When two elements combine to form two or more chemical compounds, then the masses of one of the elements which combined with a fixed mass of the other, bear a simple ratio to one another. For eg, Carbon combines with oxygen to form two compounds namely carbon dioxide and carbon monoxide.
In carbon dioxide, 12 parts by mass of carbon combine with 32 parts by mass of oxygen while in carbon monoxide, 12 parts by mass of carbon combine with 16 parts by mass of oxygen. The masses of oxygen which combined with a fixed mass of carbon in carbon monoxide and carbon dioxide are 16 and 32. These masses of oxygen bear a simple ratio of 16:32 or 1:2 to each other.
Taking another example of the Compounds of Sulphur and oxygen, we see something similar. The element sulphur also forms two oxides Sulphur dioxide and sulphur trioxide. In sulphur dioxide, 32 parts by mass of Sulphur combine with 32 parts by mass of oxygen. On the other hand, in sulphur trioxide, 32 parts by mass of Sulphur combines with 48 parts by mass of oxygen.
The masses of oxygen which combined with the fixed mass of sulphur in the two oxides are 32 and 48. These bear a simple ratio of 32:48 or 2:3 to each other.
4) Law of Reciprocal Proportion
This law was put forward by Richter in 1792. It states that “The ratio of masses of 2 elements, A and B which combines separately with a fixed mass of the third element C is either the same or some multiple of the ratio of the masses in which A and B combine directly with each other”.
For example, the elements carbon and oxygen combine separately with the third element hydrogen to form methane and water. However, they combine directly with each other to form carbon dioxide. In methane, 12 parts by mass of carbon combine with 4 parts by mass of hydrogen. In water, 2 parts by mass of hydrogen combine with 16 parts by mass of oxygen.
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The masses of carbon and oxygen which combine with a fixed mass of hydrogen are 12 and 32 ie.they are in the ratio 12:32 or 3:8. In carbon dioxide, 12 parts by mass of carbon combine directly with 32 parts by mass of oxygen ie they combined directly in the ratio of 12:32 or 3:8. This is exactly the same as the first ratio.
5) Gay Lussac’s Law of Gaseous Volume
When gases react together they always do so in volumes which bear a simple ratio to one another and to the volume of the products, if these are also gases. This holds true provided all measurements of volumes are done under similar conditions of temperature and pressure.
Solved Example for You
Q: Give an example of Gay Lussac’s Law of Gaseous Volume.
Ans: A simple example to prove the Gay Lussac’s law is that of hydrogen and chlorine. 1 volume of hydrogen and 1 volume of chlorine always combine to form two volumes of hydrochloric acid gas. The ratio between the volumes of the reactants and the product in this reaction is simple, i.e., 1:1:2.
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