Fundamental Concepts in General Chemistry

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 measurable without altering the substance's chemical identity.

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

Chemical Properties

Chemical properties describe the ability of a substance to undergo chemical changes and transform into different substances. These properties are observed during chemical reactions.

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

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

Classification of Matter

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

• Pure Substances: Have a fixed composition and distinct properties. They are further classified as:

  • Elements: Substances made of only one type of atom (e.g., Oxygen, Gold).

  • Compounds: Substances composed of two or more elements chemically combined in fixed proportions (e.g., Water (H2O), Sodium chloride (NaCl)).

• Mixtures: Combinations of two or more substances that retain their individual properties. Mixtures are classified as:

  • Homogeneous Mixtures: Uniform composition throughout (e.g., Salt solution).

  • Heterogeneous Mixtures: Non-uniform composition (e.g., Sand in water).

Matter	Pure Substance	Mixture
	Element	Homogeneous
	Compound	Heterogeneous

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 is always equal to 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 product formed.

• Equation: $\text{Total mass of reactants} = \text{Total mass of products}$

• Application: Used to balance chemical equations and understand reaction stoichiometry.

Additional info: The law of conservation of mass is foundational for quantitative chemical analysis and is a basis for other laws of chemical combination, such as the law of definite proportions.