Some Basic Concepts of Chemistry

Physical Properties

Physical properties are characteristics of a substance that can be measured or observed without changing its chemical composition. These properties help in identifying and describing substances in chemistry.

• Definition: Properties that can be measured without altering the chemical nature of the substance.

• Examples:

  • Mass

  • Volume

  • Density

Chemical Properties

Chemical properties describe the ability of a substance to undergo chemical changes and transform into different substances. These properties are evaluated by observing the chemical reactions of the material.

• Definition: Properties that can be evaluated at the cost of matter itself, involving a change in chemical composition.

• Examples:

  • Reactivity with acids or bases

  • Flammability

  • Oxidation states

Classification of Matter

Matter is anything that has mass and occupies space. In chemistry, matter is classified based on its composition and properties.

• Main Categories:

  • Pure Substance

    • Element: A substance made up of only one kind of atom. Example: Oxygen (O2), Gold (Au)

    • Compound: A substance composed of two or more different elements chemically combined in fixed proportions. Example: Water (H2O), Sodium chloride (NaCl)

  • Mixture

    • Homogeneous Mixture: Composition is uniform throughout. Example: Salt dissolved in water

    • Heterogeneous Mixture: Composition is not uniform; different parts can be seen. Example: Sand and iron filings

Law of Chemical Combination

Law of Conservation of Mass

The law of conservation of mass is a fundamental principle in chemistry stating that mass is neither created nor destroyed in a chemical reaction. The total mass of reactants equals the total mass of products formed.

• Statement: For any chemical change, the total mass of active reactants is always equal to the mass of the products formed.

• Mathematical Expression:

• Example: When hydrogen reacts with oxygen to form water:

  • Mass of hydrogen + mass of oxygen = mass of water produced

Additional info: The law of conservation of mass is the basis for balancing chemical equations and is essential for quantitative chemical analysis.