BackFundamental Concepts in General Chemistry: Properties, Classification of Matter, and Laws of Chemical Combination
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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 substance's chemical composition.
Definition: Properties such as mass, volume, and density that do not alter the identity of the substance when measured.
Examples: Mass, volume, density, melting point, boiling point, color, and state of matter.
Chemical Properties
Chemical properties describe a substance's ability to undergo changes that transform it into different substances.
Definition: Properties that can only be observed or measured by changing the chemical identity of a substance.
Examples: Reactivity with acids, flammability, ability to rust, and combustibility.
Classification of Matter
Matter can be classified based on its physical and chemical composition. The main categories are pure substances and mixtures.
Matter
Pure Substance: Has a fixed composition and distinct properties. Can be further classified as:
Element: A substance that cannot be broken down into simpler substances by chemical means (e.g., hydrogen, oxygen).
Compound: A substance composed of two or more elements chemically combined in a fixed ratio (e.g., water, carbon dioxide).
Mixture: Consists of two or more substances physically combined. Can be further classified as:
Homogeneous Mixture: Has a uniform composition throughout (also called a solution; e.g., salt water, air).
Heterogeneous Mixture: Does not have a uniform composition; different parts can be seen (e.g., salad, sand in water).
Type | Definition | Examples |
|---|---|---|
Element | Cannot be broken down into simpler substances | O2, Fe, H2 |
Compound | Composed of two or more elements chemically combined | H2O, CO2 |
Homogeneous Mixture | Uniform composition throughout | Salt water, air |
Heterogeneous Mixture | Non-uniform composition | Sand in water, salad |
Law of Chemical Combination
Law of Conservation of Mass
The law of conservation of mass is a fundamental principle in chemistry that states that mass is neither created nor destroyed in a chemical reaction.
Statement: For any chemical change, the total mass of the reactants is always equal to the total mass of the products formed.
Mathematical Expression:
Example: When hydrogen reacts with oxygen to form water:
2 g of hydrogen + 16 g of oxygen → 18 g of water
Total mass before reaction = 18 g; total mass after reaction = 18 g
Additional info: The law of conservation of mass was first formulated by Antoine Lavoisier in the late 18th century and is foundational to all chemical equations and stoichiometric calculations.
