Laws of Chemical Combination

Chemistry is governed by fundamental principles that explain how elements combine to form compounds. These are known as the laws of chemical combination.  

1. Law of Conservation of Mass  

- Also called the law of conservation of matter.  

- States that the mass before and after a reaction remains the same, provided no loss occurs.  

- Quote:  

  “Matter can neither be created nor destroyed during a chemical reaction but changes from one form to another.”  

2. Law of Definite Proportion (Law of Constant Composition)  

- A pure chemical compound always contains the same elements combined in a fixed ratio by mass, regardless of source or method of preparation.  

- Quote:  

  “All pure samples of a particular chemical compound contain similar elements combined in the same proportion by mass.” 

3. Law of Multiple Proportion  

- If two elements (A and B) combine to form more than one compound, the masses of one element (A) that combine with a fixed mass of the other (B) are in simple whole‑number ratios.  

- Example: Carbon and oxygen form both CO and CO₂. The ratio of oxygen masses combining with a fixed mass of carbon is 1:2.  

4. Law of Reciprocal Proportion  

- If elements A, B, and C separately combine with a fixed mass of another element D, then the masses in which A, B, and C combine with each other are either the same or simple multiples of the masses in which they combine with D.