Laws of Chemical Combination for Elements and Compounds - Meaning, Definition, Examples, FAQs

Chemistry is the study of the transformation of a story from one genre to another. These changes often occur as a result of a combination of two types of story. There are certain rules that govern the integration of different substances to form different compounds. These laws are, as we call them, laws of chemical compounds. There are five basic Law of Chemical combination of Elements and Compounds of chemical composition that control chemical composition.

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This Story also Contains

1. The laws of chemical combination.
2. Some Solved Examples
3. Summary

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The laws of chemical combination.

Law of Conservation of Mass :

It states that Matter can neither be created nor destroyed. This law formed the basis for several later developments in chemistry. In fact, this was the result of the exact measurement of masses of reactants and products, and carefully planned experiments performed by Lavoisier.

Law of Definite Proportions :

This law was given by, a French chemist, Joseph Proust. He stated that a given compound always contains exactly the same proportion of elements by weight.

Law of Multiple Proportions :

This law was proposed by Dalton in 1803. According to this law, if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers.

Gay Lussac’s Law of Gaseous Volumes :

This law was given by Gay Lussac in 1808. He observed 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.

Avogadro Law :

• According to this law, "Under similar conditions of temperature and pressure, the equal volume of gases the equal number of molecules. "

It means 10 ml of H₂, O₂, N₂ or a mixture of gases have the same number of molecules.

It is used in:

(i) The deriving molecular formula of a gas

(ii) Determining atomicity of a gas

(iii) Deriving a relation

molecular mass = 2 x vapour density

M=2 X VD

(iv) Deriving the gram molecular volume

• Avogadro number (N_o or N_A) = 6.023 x 10²³
• Avogadro number of gas molecules occupy 22.4 litre or 22400 ml or cm³ volume at STP
• The number of molecules in 1 cm³ of a gas at STP is equal to Loschmidt number, that is, 2.68 x 10¹⁹
• The reciprocal of Avogadro number is known as Avogram.

Related Topics,

• Law Constant Proportion
  
• Balancing Chemical Equations
• Mole Concept Basics
• Difference Between Physical and Chemical Change
• Difference Between Compound and Mixture

Recommended topic video on (Laws of Chemical Combination for elements)

Some Solved Examples

Example.1

The ratio of masses of oxygen and nitrogen in a particular gaseous mixture is 1:4. The ratio of a number of their molecule is :

1) 1 : 4

2) 7 : 32

3)1 : 8

4)3 : 16

Solution

We know

Mole = mass/molar mass

Avogadro's number is defined as the number of elementary particles (molecules, atoms, compounds, etc.) per mole of a substance. It is equal to 6.022×10²³ mol^-1 and is expressed as the symbol N_A.

Now let the ratio be m, therefore, the mass of O₂ is m and the mass of N₂ is 4m.
Therefore, moles of O₂ = m/32 and moles of N₂ = 4m/28

Thus, $\frac{\text { molecules }_{\mathrm{O}_2}}{\mathrm{molecules}_{\mathrm{N}_2}}=\frac{\frac{\mathrm{m}}{32} \times \mathrm{N}_{\mathrm{A}}}{\frac{4 \mathrm{~m}}{28} \times \mathrm{N}_{\mathrm{A}}}=\frac{7}{32}$

Hence, the answer is the option (2).

Example. 2

What is the ratio of masses of oxygen that combine with a fixed mass of Hydrogen in water and Hydrogen Peroxide?

1) (correct)1 : 2

2)2 : 1

3)2 : 3

4)3 : 2

Solution

As we learnt in

$\mathrm{H}_2+\frac{1}{2} \mathrm{O}_2 \rightarrow \mathrm{H}_2 \mathrm{O}$

2g 16g 18g

$\mathrm{H}_2+\mathrm{O}_2 \rightarrow \mathrm{H}_2 \mathrm{O}_2$

2g 32g 34g

One mole of water has 2g hydrogen & 16g oxygen.

Similarly, one mole of hydrogen peroxide has 2g of hydrogen and 32 g of oxygen

Therefore, masses of oxygen combined with a fixed mass of hydrogen in water and hydrogen peroxide have a ratio of 16:32 = 1:2

the ratio = $\frac{16 g}{32 g}=\frac{1}{2}$

Hence, the answer is the option (1).

Example .3

What is the ratio of the masses of oxygen that combine with a fixed value of nitrogen in the compounds nitrogen monoxide and nitrogen dioxide?

1)2 : 3

2)2 : 1

3)3 : 2

4) (correct)1 : 2

Solution

Let's take NO first, the chemical reaction follows:

$N_2+O_2 \rightarrow N O$

$\frac{\text { Mass of } N}{\text { mass of } O}=\frac{14}{16}=1: 1.143$

in NO₂,

$2 \mathrm{NO}+\mathrm{O}_2 \rightarrow 2 \mathrm{NO}_2$

there are 2 N and 4 O in the reaction,

$\frac{\text { Mass of } N}{\text { mass of } O}=\frac{28}{64}=1: 2.286$

$\therefore \frac{\text { Mass of } \mathrm{O} \text { in } \mathrm{NO}}{\text { mass of } \mathrm{O} \text { in } \mathrm{NO}_2}=\frac{1.143}{2.286}=1: 2$

Hence, the answer is the option (4).

Also check-

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NCERT Chemistry Notes:

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Summary

This law based on the principle how the atoms or elements combines to form the compounds. there are several law connected to each other to form the law of chemical composition on the basis of their proportions.