## Laws of Chemical CombinationThere are certain rules or laws in chemistry that all chemical reactions follow when they occur. These laws are called the laws of chemical combination. These laws are exclusively for chemical reactions in which electrons of elements are involved. The nuclear reactions do not follow these laws as the nucleus is involved in the nuclear reactions. There are mainly ## 1) Law of Conservation of Mass or (law of indestructibility of Matter)This law was given by So, according to this law, the reactants when consumed completely or converted completely into products, the sum of masses of reactants will be equal to the sum of masses of products, which means the total mass of reactants = total mass of products. Due to this reason, we are required to balance a chemical equation. If the reactants are not converted into products completely, Total mass of reactants = total mass of products + mass of unreacted reactants For example, in the following chemical reaction, one molecule of hydrogen reacts with one molecule of chlorine to form 2 molecules of hydrogen chloride (HCl). H In the above chemical reaction, the atomic mass of hydrogen is 2 g as there are 2 atoms of hydrogen, and the atomic mass of chlorine is 71 as there are two atoms of chlorine. So, reactants' total mass is 2 + 71 = 73 g. Now, in this reactions, 2 molecules of hydrogen chloride (HCl) are formed, whose total mass is 2 (1x 35.5), which is equal to the total mass of reactants. It shows this reaction follows the law of conservation of mass as mass is neither created nor destroyed, it is just converted from one form to another form. Besides this, in this reaction, the reactants are completely consumed to form the products, so reactants' total mass = products' total mass. ## 2) Law of Definite Proportion or Law of Constant CompositionThis law was given by For example, you can take water from any source or prepare it by any method, the ratio of hydrogen and oxygen atoms in a molecule of water by weight remains fixed or the same (H ## 3) Law of Multiple ProportionsThis law was given by
Hydrogen and oxygen form two different compounds water (H
Carbon and oxygen react with each other to form carbon dioxide (CO
Nitrogen combines with oxygen to form the following compounds. - N
_{2}O (weight of nitrogen is 28, weight of oxygen is 16) - NO (weight of nitrogen is 14, weight of oxygen is 16)
- NO
_{2}(weight of N is 14 and weight of 32) - N
_{2}O_{3}(weight of N is 28 and weight of 48) - N
_{2}O_{5}( weight of N is 28 and weight of O is 80)
If we take two moles of NO and NO Now, we have a fixed weight of N (28 gm) in all molecules and O is reacting with a fixed weight of Nitrogen. Now according to this law, the ratio of different masses of oxygen to each other in these different molecules should be a simple whole-number ratio, which is 16: 32: 64: 48: 80 or 1: 2: 4: 3: 5. ## 4) Law of Reciprocal ProportionsIt was first formulated by
Suppose there are three elements P, Q, and R. X gm of P combines with Y gm of Q to form PQ Z gm of R combines with Y gm Q to form ZQ Here, the ratio of the masses of P and R that combines with the fixed mass (Y gm) of Q = X: Z Now, U gm of P combines with V gm of R, to form PR, so their ratio when they combine with each other = U: V Now according to this law, the ratio of P and R (X: Z) when they combine with a fixed mass of the third element is equal to or multiple of their ratio (U: V) when they combine with each other. So, either X: Z = U: V or X: Z = n times of U: V where, n can be 1, 2, 3, etc.
Hydrogen forms water (H Now the ratio of masses of S: O when combine differently is 32: 16 = 2: 1 Now, the ratio of S: O when they combine with each other: 32: 32 = 1: 1 Now as per the law the ratio 2:1 should be equal to 1:1 or multiple of 1:1. In this case it is a multiple of 1:1 as 2:1 = 1:1 x 2 ## 5) Law of Gaseous VolumeThis law was given by
In the following example, one volume of hydrogen gas combines with one volume of chlorine gas to form 2 volumes of hydrogen chloride gas. H So, as per the law of gaseous volume, the ratio of their volumes that are combining would be simple a simple ratio, in this case, the ratio is 1: 1: 2. Let us take another example to understand it: N Here, one volume of nitrogen gas combines with 3 volumes of hydrogen gas to form 2 volumes of ammonia. Now, in this case, also, the ratios of volumes of reactants and product is a simple ratio (1: 3: 2), which follows the law of gaseous volume. Next TopicStoichiometry |