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The laws of chemical combinations are related to the laws that govern the combining of different elements to produce different compounds.
- Chemistry is the study of the transformation of matter from one form to another.
- These changes are generally caused by the interaction of two different types of matter.
- Certain laws control the combination of different elements to produce various chemical compounds.
- These are known as the laws of chemical combinations.
| Table of Content |
Key Terms: Atoms, Molecules, Chemical combination Laws, 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
Laws of Chemical Combination
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Chemistry is often concerned with chemical reactions in which multiple elements combine to form a single compound. There are 5 laws of chemical combination that govern the chemical reaction. These 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
Also check:
| Related Concepts | ||
|---|---|---|
| Displacement Reactions | Combined Gas Law | Some Basic Concepts of Chemistry |
| Oxidation and Reduction | Corrosion | Rancidity |
Law of Conservation of Mass
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The law of conservation of mass states that "mass cannot be created or destroyed; it can only be transformed from one form to another."
- Antonie Lavoisier proposed this in 1789, based on the results obtained from several combustion reactions.
- It states that the total mass of the product obtained by chemical combination equals the sum of the masses of all reactants involved.
Example of Law of Conservation of MassExample: The heating of calcium carbonate (10 grams) produces calcium oxide (5.6 grams) and calcium dioxide (4.4 grams). calcium carbonate (10 grams) → calcium oxide (5.6 grams) + calcium dioxide (4.4 grams) According to the law of conservation of mass, Total mass of reactants = Total mass of products Here
Therefore, 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
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The law of definitive proportions states that “elements are always combined in specific definite proportions”.
- It indicates that elements always combine in a specific ratio, regardless of the number of reactants used or the source from which they were obtained.
- In 1799, Joseph Proust introduced the concept of definite proportions.
- This law is also known as Proust's law or law of constant proportions.
Example of Law of Definite ProportionsExample: Ethyl alcohol (C2H5OH) According to the law of constant proportions, regardless of the total amount of ethyl alcohol present, its composition is 52% carbon, 35% oxygen, and 13% hydrogen by weight. |
Law of Multiple Proportions
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In 1804, John Dalton proposed the law of multiple proportions.
According to the law of multiple proportions, when the same two elements combine to form more than one compound, the different masses of an individual element that combine with the same mass of the other elements exist in the ratio of small whole numbers.
Example of Law of Multiple ProportionsExample: Consider the atoms of carbon and oxygen.
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Gay Lussac’s Law of Gaseous Volumes
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Gay Lussac's law of gaseous volumes states that the ratio of all gaseous reactants and products can be expressed in small whole numbers.
- In 1808 Gay Lussac proposed the law of gaseous volumes.
- When gases react at a specific pressure and temperature, the ratio of reactant to product volumes is easily expressed in small whole numbers.
Example of Gay Lussac’s Law of Gaseous VolumesExample: Gay Lussac's law of gaseous volumes governs the reaction of hydrogen gas with chlorine gas. H2 + Cl2 → 2 HCl In this example, one volume of hydrogen gas and one volume of chlorine gas mix to form two volumes of HCl gas. The volume ratios of hydrogen gas, chlorine gas, and HCl are 1:1:2. |
Avagadro’s Law of Chemical Combination
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In 1811, Avagadro proposed the fifth law of chemical combination.
According to Avagadro’s law of chemical combination, at a particular temperature and pressure, the volume of gaseous molecules is directly proportional to the total number of moles.
It can be expressed as
V ∝ n or V = k x n
Where
- V is the volume of gaseous molecules
- n is the total number of moles of the gas
- k is the proportionality constant
The above equation can also be written as,
\(\frac {V_1}{n_1}=\frac {V_2}{n_2}\)
Where
- V1 is the volume and n1 is the number of moles of one gas.
- V2 is the volume and n2 is the number of moles of another gas.
Example of Avagadro’s Law of Chemical CombinationExample: Blowing a balloon with helium gas. The overall volume of the balloon increases as the total number of moles of helium gas blown into it increases. |
Also check:
| Equilibrium | Chemical Formula | Physical and Chemical Classification of Matter |
| Solutions | MCQ On Some Basic Concepts of Chemistry | Raoult's Law |
Things To Remember
- The laws of chemical combination govern how elements interact to form compounds.
- The law of conservation of mass states that mass cannot be created nor be destroyed.
- The law of definite proportions states that elements are always combined in specific definite proportions.
- Gay Lussac's law of gaseous volumes states that the ratio of all gaseous reactants and products can be expressed in small whole numbers.
- Avagadro's law states that the volume of gaseous molecules is directly proportional to the total number of moles.
Sample Questions
Ques. What is the Law of Chemical Combination? (1 Mark)
Ans. The laws of chemical combinations are related to the principles that regulate the combination of various elements to form various compounds.
Ques. What does fixed proportions mean in the context of chemical combinations? (1 Mark)
Ans. It means that the masses of the elements in a compound are always in simple whole-number ratios.
Ques. Can the Law of Chemical Combination be applied to all types of compounds? (1 Mark)
Ans. Yes, the law is a fundamental law that applies to all chemical compounds, simple or complex.
Ques. What is Gay Lussac’s law? Give an example of Gay Lussac’s Law of Gaseous Volume. (3 Marks)
Ans. Gay Lussac's law of gaseous volumes states that the ratio of all gaseous reactants and products can be expressed in small whole numbers.
The hydrogen and chlorine example is a simple way to demonstrate Gay Lussac's law. Hydrochloric acid gas is always formed when one volume of hydrogen and one volume of chlorine are combined. In this reaction, the volume ratio between the reactants and the product is simple, i.e. 1:1:2.
Ques. Define the law of conservation of mass with an example. (2 Marks)
Ans. In a chemical process, the law of conservation of mass states that matter cannot be generated or destroyed.
For example, when wood burns, the mass of soot, ashes, and gases equals the mass of charcoal and oxygen when it initially reacts. As a result, the mass of the product and the mass of the reactant are equal.
Ques. Define the law of definite proportion with an example. (2 Marks)
Ans. The Law of Definite Proportions states that whatever the amount or source, a chemical compound will always have the same proportions or amount of each element by weight. A 50-gram sample of carbon monoxide, for example, will contain 21.5 g of carbon and 28.5 g of oxygen.
Ques. Define the law of multiple proportions with an example. Why is it important? (3 Marks)
Ans. The law of multiple proportions states that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other element will always be in a simple ratio of small whole numbers.
Example: Carbon can form two oxides: carbon monoxide (CO) and carbon dioxide (CO₂). In CO, 12 grams of carbon combine with 16 grams of oxygen. In CO₂, 12 grams of carbon combine with 32 grams of oxygen. The ratio of oxygen mass in these compounds is 16:32, which simplifies to 1:2.
Ques. Explain any two applications of Gay Lussac’s Law. (3 Marks)
Ans. The two applications of Gay Lussac’s Law are
- Gay Lussac's Law governs the cooking of food in pressure cookers (the relationship between temperature and pressure).
When we apply heat to the pressure cooker, the water vaporizes and becomes steam. The steam has sufficient thermal energy to cook the meal.
- Gay Lussac's Law causes a tire blowout as a direct result.
On a hot sunny day, the pressure of the gas inside the tyre rises as the temperature of the surrounding air rises, exerting pressure on the tire walls. As a result, the tyre bursts after a particular threshold is reached.
Ques. What is the importance of Gay Lussac’s Law? (2 Marks)
Ans. This gas law is significant because it depicts the relationship between pressure and temperature in a gas sample when the volume remains constant. An increasing gas's temperature causes a relative increase in its pressure, according to this Law (assuming that the volume does not change). Similarly, lowering the temperature lowers the pressure imposed on the container's walls.
Ques. What are the limitations of Avogadro's law? (2 Marks)
Ans. Even though Avogadro's rule is entirely applicable to ideal gases, it only yields approximate relationships at best. Furthermore, at high pressures and low temperatures, the deviation of real gases from ideal behavior increases. "Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules," according to Avogadro's law. If the temperature and pressure remain constant, the volume and amount (moles) of an ideal gas are directly proportional to its mass.
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