Chemical substance

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Potassium-ferricyanide-sample

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Chemical substance refers to a form of matter having constant chemical composition and characteristic properties. It can exist in the solid, liquid, or gas phase, and can change between these phases through physical processes like melting, freezing, and evaporation. A chemical substance can be a pure chemical element or a pure chemical compound consisting of two or more elements that are chemically bonded together.

Definition and Characteristics

A chemical substance is defined by its uniform composition and specific set of properties, distinguishing it from a mixture, where the composition can vary. For example, pure water (H₂O) is a chemical substance because it has a consistent composition and set of properties, whereas seawater, which contains various salts dissolved in water, is a mixture.

Classification

Chemical substances can be classified into two main categories: chemical elements and chemical compounds. Chemical elements, such as oxygen and iron, consist of only one type of atom and cannot be broken down into simpler substances by chemical means. Chemical compounds, such as water and sodium chloride (table salt), consist of two or more elements that are chemically combined in fixed proportions.

Pure Substances and Mixtures

A pure substance has a uniform and definite composition, whereas a mixture has a composition that can vary depending on the proportions of its components. Mixtures can be homogeneous or heterogeneous. A homogeneous mixture has the same composition throughout, while a heterogeneous mixture's composition can vary within the sample.

Properties

Chemical substances have both physical properties and chemical properties. Physical properties, such as melting point, boiling point, and density, can be observed or measured without changing the substance's chemical identity. Chemical properties, such as reactivity with other chemicals, describe how a substance interacts with other substances to form new substances.

Identification

Chemical substances are identified by specific names and chemical formulae that reflect their composition. For example, the chemical formula for water, H₂O, indicates that each molecule consists of two hydrogen atoms and one oxygen atom. The International Union of Pure and Applied Chemistry (IUPAC) provides standardized naming conventions for chemical substances.

Regulation and Safety

The use and handling of chemical substances are regulated by laws and regulations to ensure safety and protect health and the environment. Material Safety Data Sheets (MSDS) provide information on the properties, health hazards, and safe handling practices of chemical substances.

Applications

Chemical substances are essential in various industries, including pharmaceuticals, agriculture, manufacturing, and energy production. They play a crucial role in the development of medications, fertilizers, plastics, and other materials that are integral to modern life.