Compare

To compare and describe chemicals, one must

look at their unique physical and chemical properties, as all chemicals are distinct forms of matter with specific, defined compositions.

Describing Chemicals

A chemical is any substance with a defined and constant composition, such as water (

H2OH sub 2 O

H2O

) or salt (sodium chloride, NaCl). Everything that takes up space (matter) is made of chemicals, but phenomena like light or energy are not.

Chemicals are described and identified by their characteristic properties:

Physical Properties: These can be observed or measured without changing the substance’s chemical composition.
- Examples: Color, mass, volume, density, melting point, boiling point, hardness, and electrical conductivity.
Chemical Properties: These describe a substance’s ability to react with other substances to form new, different substances. Observing a chemical property always involves a chemical change.
- Examples: Flammability, toxicity, chemical stability, and susceptibility to corrosion (like iron rusting in air).

Comparing Chemicals

Chemicals are compared based on how their properties differ, which determines how they will interact:

Physical Compatibility: Two chemicals can be physically mixed without forming a new substance (e.g., salt dissolving in water, which can be separated by evaporation).
Chemical Compatibility/Reactivity: When mixed, incompatible chemicals can cause a chemical reaction, forming a new substance with new properties. This is crucial for safe storage and handling, as mixing incompatible chemicals can cause fires, explosions, or toxic gas production.

For safe handling, chemicals are often grouped into general categories for comparison, such as:

Chemists use systematic rules developed by organizations like the International Union of Pure and Applied Chemistry (IUPAC) to name and classify compounds, ensuring clear and consistent comparisons worldwide.