What Are Chemicals?

Chemicals are pure substances or mixtures of substances with defined composition and properties, produced by or used in chemical processes. They range from simple elements such as hydrogen and nitrogen to complex polymers, pharmaceuticals, and specialty reagents used in advanced manufacturing. In engineering and applied science, the term encompasses industrial feedstocks, reagents, solvents, and materials whose physical and chemical properties determine their suitability for a given process or product.

Chemistry as a discipline classifies substances by their elemental composition, molecular structure, and reactivity. Organic chemicals are those based on carbon frameworks, including hydrocarbons, alcohols, acids, and polymers derived from petroleum or biomass. Inorganic chemicals encompass metals, salts, oxides, and acids that do not carry carbon-hydrogen bonds as their central structural feature. This division underpins two broad branches of industrial chemical production and research.

Classification and Properties

Chemicals are classified by several overlapping schemes: by composition (elements, compounds, mixtures), by origin (natural, synthetic, or semi-synthetic), and by function (acids, bases, solvents, oxidizers, reducing agents, catalysts). Physical properties including melting point, boiling point, solubility, density, and vapor pressure govern how a chemical behaves during processing and storage. Chemical properties describe how a substance transforms through reactions: its reactivity toward oxygen, water, acids, or other reagents. The NIST Chemistry WebBook is a reference database compiled by the National Institute of Standards and Technology that provides thermochemical, spectroscopic, and physical property data for tens of thousands of compounds, and is the standard starting point for engineers selecting process chemicals.

Chemical Synthesis and Production

Industrial chemical production converts raw materials such as petroleum fractions, natural gas, coal, and mineral ores into value-added products through controlled reaction sequences. The Haber-Bosch synthesis of ammonia from nitrogen and hydrogen, developed in the early twentieth century, remains the largest-scale synthetic chemical process by volume, producing the nitrogen fertilizers that support global food production. Catalysis is central to most large-scale synthesis routes: heterogeneous catalysts accelerate reactions at solid surfaces while remaining in a separate phase from the reactants, enabling continuous processing and easy catalyst recovery. Green chemistry principles, codified by Anastas and Warner in 1998, direct synthesis toward atom-efficient reactions, renewable feedstocks, and minimal byproduct generation. The PMC review on mechanochemistry for organic and inorganic synthesis describes how solvent-free mechanical activation of reagents can replace conventional solution-phase routes, reducing waste and energy consumption.

Hazard, Regulation, and Safety

The physical and chemical properties of a substance determine its hazard profile: flammability, toxicity, corrosivity, and reactivity toward air or water. Internationally, the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) standardizes hazard categories and safety data sheet formats across regulatory jurisdictions. Exposure limits for workplace environments are set by agencies such as OSHA in the United States and REACH regulations in the European Union. NIST's Chemical Safety data resources support hazard assessment for both pure substances and mixtures used in research and industrial settings.

Applications

Chemicals have applications in a wide range of industries, including:

• Semiconductor and electronics manufacturing, where high-purity reagents are essential
• Pharmaceutical production and drug formulation
• Agricultural fertilizers, herbicides, and pesticides
• Polymer and plastics manufacturing
• Energy storage and fuel cell materials
• Water treatment and environmental remediation