Some Basic Concepts of Chemistry

Physical Properties

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

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

• Examples: Mass, volume, density, melting point, boiling point.

• Application: Used in physical separation techniques and in identifying substances.

Chemical Properties

Chemical properties describe the ability of a substance to undergo chemical changes or reactions, resulting in the formation of new substances.

• Definition: Properties that can be evaluated only by changing the chemical composition of matter.

• Examples: Reactivity with acids, flammability, oxidation states.

• Application: Important in chemical synthesis and predicting chemical behavior.

Classification of Matter

Matter is anything that has mass and occupies space. It can be classified based on its composition and properties.

• Main Categories:

  • Pure Substance

    • Element: A substance made up of only one kind of atom. Cannot be broken down into simpler substances by chemical means. 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 solution, air.

    • Heterogeneous Mixture: Composition is not uniform; different parts have different compositions. Example: Sand and iron filings, salad.

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.

• Equation:

• Example: When hydrogen reacts with oxygen to form water: The mass of hydrogen and oxygen used equals the mass of water produced.

• Application: Used in stoichiometric calculations and balancing chemical equations.

Additional info: The Law of Conservation of Mass was first formulated by Antoine Lavoisier in the 18th century and is foundational for all chemical reactions and processes.