Fundamental Chemical Laws: Conservation, Atoms & Mole Concepts

Chemical Reaction

Chemical reaction is a process by which one or more substances become another or different.

Lavoisier — Conservation of Mass

Lavoisier's law or conservation of mass: The mass of a system remains constant, regardless of the transformation that occurs within it. In any chemical transformation that takes place in a closed system, the total mass of the substances present is conserved.

Proust — Law of Definite Proportions

Proust and the law of constant proportions: When two or more elements combine to give the same compound, they always do so in definite and constant mass proportions. This law allows us to distinguish compounds from homogeneous mixtures: a homogeneous mixture can be formed by the same components as a compound but in different proportions; a compound has a single and unchanging proportion. The ratio of the mass of copper to the mass of sulfur in all cases is: copper mass / sulfur mass = 4.

Dalton's Atomic Theory

Dalton's theory:

• Matter consists of indivisible atoms.
• The atoms are unchanged in chemical reactions.
• Elements consist of identical atoms.
• Atoms of different elements have different masses and chemical properties.
• Chemical compounds are formed by combining two or more atoms of different elements.
• When atoms of different elements combine to form a compound, they do so in simple integer ratios.
• In chemical reactions the atoms only change the distribution of substances.

Element

Element: A substance formed by like atoms.

Compound

Compound: A substance formed by different atoms combined in fixed proportions.

Gay-Lussac's Law of Combining Volumes

Gay-Lussac on the volumes of gases: He observed that 2 volumes of hydrogen combine exactly with 1 volume of oxygen to form 2 volumes of water vapor, provided that all gases are measured under the same conditions of pressure and temperature: 2 vol H2 + 1 vol O2 = 2 vol H2O (vapor).

Avogadro's Law

Avogadro's law: Avogadro proposed a hypothesis in two points:

1. The particles of gases are not atoms but aggregates of atoms equal to those we call molecules.
2. Equal volumes of gases, measured under the same conditions of temperature and pressure, contain the same number of molecules.

Amount of Substance (Mole)

Amount of substance (n): The amount of substance, n, is a quantity whose SI unit is the mole (mol). The mole is a group of 6.022 × 10²³ identical particles. These may be atoms, molecules, ions, electrons, or other particles or specific groupings of them. This number is called Avogadro's number (or Avogadro's constant) in honor of the scientist.

Molar Volume

Molar volume is the volume occupied by one mole of a gas measured at 273 K and 1 atm. The molar volume of all ideal gases at 273 K and 1 atm is 22.4 L. In 22.4 L of any gas, measured at 273 K and 1 atm, there are 6.022 × 10²³ atoms or molecules.