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 that can be measured without altering the chemical identity of a substance.

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

• Application: Used to distinguish substances and to separate mixtures by physical means.

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 identity of the substance.

• Examples: Reactivity with acids, flammability, oxidation states, ability to rust.

• Application: Used to predict how substances will react and what products will form.

Classification of Matter

Types of Matter

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

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

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

  • Compound: A substance composed of two or more different elements chemically combined in a fixed ratio. Example: Water (H2O)

• Mixtures: Consist of two or more substances physically combined. They can be separated by physical means and are classified as:

  • Homogeneous Mixture: Has uniform composition throughout. Example: Salt solution

  • Heterogeneous Mixture: Has non-uniform composition. Example: Sand and iron filings

Type	Subcategory	Example
Pure Substance	Element	Gold (Au)
Pure Substance	Compound	Water (H2O)
Mixture	Homogeneous	Air
Mixture	Heterogeneous	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 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:

$\text{Total mass of reactants} = \text{Total mass of products}$

• Example: When hydrogen reacts with oxygen to form water: $2H_2 + O_2 \rightarrow 2H_2O$ The mass of hydrogen and oxygen used equals the mass of water produced.

Additional info: The law of conservation of mass is foundational for stoichiometry and balancing chemical equations in chemistry.