Chemical phenomena

Chemical phenomena are observable events involving substances’ properties, composition, or transformations. They include reactions, phase changes, and interactions between matter and energy.

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Matter: Matter is physical substance that has mass and occupies space. Chemical phenomena occur in matter, whose particles and properties can be observed or changed.
Chemical reaction: A chemical reaction transforms reactants into products by reorganizing atoms and changing chemical bonds. Reactions are the central class of phenomena that change substances’ composition.
Combustion: Combustion is a rapid exothermic reaction, commonly involving a fuel and an oxidizer. Flames and heat make this familiar chemical transformation directly observable.
Physical change: A physical change alters a material’s form or state without changing its chemical composition. It contrasts with reactions that produce substances with different compositions.
Atom: An atom is the smallest unit of an element that retains its chemical identity. Atoms are rearranged in chemical reactions while their nuclei generally remain unchanged.
Chemical kinetics: Chemical kinetics studies the rates and mechanisms of chemical reactions. Reaction rates determine how quickly a chemical change becomes observable.
Electrochemistry: Electrochemistry studies chemical processes involving electron transfer and electrical energy. It links reactions to batteries, corrosion, and electrical measurements.
Phase transition: A phase transition is a change between states of matter, such as melting or boiling. It can look dramatic while leaving the substance’s chemical identity intact.
Molecule: A molecule is a group of atoms held together by chemical bonds. Molecular structure helps determine the properties and reactions of many substances.
Chemical equilibrium: Chemical equilibrium is a dynamic state in which forward and reverse reaction rates are equal. Equilibrium explains why some chemical changes stop showing net progress.