BackFundamental Concepts in General Chemistry
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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.
Definition: Properties such as mass, volume, and density are considered physical properties.
Examples: Measuring the boiling point or melting point of water does not alter its chemical identity.
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 only be evaluated by changing the chemical identity of the substance are called chemical properties.
Examples: Reactivity with acids, flammability, and oxidation are chemical properties.
Classification of Matter
Matter can be classified based on its composition and uniformity. The main categories are pure substances and mixtures.
Pure Substance: Matter with a fixed composition. It can be further divided into:
Element: A substance made of only one kind of atom (e.g., oxygen, gold).
Compound: A substance composed of two or more elements chemically combined in fixed proportions (e.g., water, sodium chloride).
Mixture: Matter that consists of two or more substances physically combined. Mixtures can be:
Homogeneous Mixture: Uniform composition throughout (e.g., saltwater).
Heterogeneous Mixture: Non-uniform composition (e.g., sand and iron filings).
Type | Subcategories | Examples |
|---|---|---|
Pure Substance | Element, Compound | Oxygen (Element), Water (Compound) |
Mixture | Homogeneous, Heterogeneous | Saltwater (Homogeneous), Sand & Iron (Heterogeneous) |
Law of Chemical Combination
Law of Conservation of Mass
The law of conservation of mass states that in any chemical reaction, the total mass of the reactants is always equal to the total mass of the products formed.
Definition: Mass is neither created nor destroyed during a chemical reaction.
Equation:
Example: When hydrogen reacts with oxygen to form water, the combined mass of hydrogen and oxygen before the reaction equals the mass of water produced.
Additional info: The law of conservation of mass is fundamental to stoichiometry and chemical equations in chemistry.
