Detailed Summary
The Law of Constant Proportions, also known as the Law of Definite Proportions, asserts that chemical compounds consist of elements that combine in specific, constant mass ratios regardless of their source or method of preparation. This principle emerged from the observations of early chemists like Lavoisier and was formally articulated by Proust, stating: “In a chemical substance, the elements are always present in definite proportions by mass.â€
For instance, in every sample of water (H₂O), the mass ratio of hydrogen to oxygen is always 1:8, and in ammonia (NH₃), nitrogen and hydrogen are consistently found in a 14:3 ratio by mass.
The development of this law set the stage for John Dalton's atomic theory, proposing that all matter is composed of atoms—indivisible particles that combine in simple whole-number ratios to form compounds. Dalton's postulates detail various aspects of atomic theory, including that:
- All matter consists of tiny particles called atoms.
- Atoms cannot be created or destroyed in chemical reactions.
- All atoms of a given element are identical in mass and properties.
- Different elements have atoms of different masses.
- Atoms combine in fixed ratios to form compounds.
This foundation confirms both the law of conservation of mass and the law of constant proportions, emphasizing the structural rules governing chemical combinations.