A starting material in a chemical reaction.

A material resulting from a chemical reaction.

The making and breaking of chemical bonds, leading to changes in the composition of matter.

In a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative concentrations of the reactants and products do not change with time.

A molecule (such as water) with opposite charges on different ends of the molecule.

The binding together of like molecules, often by hydrogen bonds.

The attraction between different kinds of molecules.

A measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules.

The total amount of kinetic energy due to the random motion of atoms or molecules in a body of matter; also called thermal energy. Heat is energy in its most random form.

A measure of the intensity of heat in degrees, reflecting the average kinetic energy of the molecules.

The amount of heat energy required to raise the temperature of 1 g of water by 1°C; also the amount of heat energy that 1 g of water releases when it cools by 1°C. The Calorie (with a capital C), usually used to indicate the energy content of food, is a kilocalorie.

A thousand calories; the amount of heat energy required to raise the temperature of 1 kg of water by 1°C.

A unit of energy: 1 J = 0.239 cal; 1 cal = 4.184 J.

The amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature by 1°C.

The quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.

The process in which the surface of an object becomes cooler during evaporation, owing to a change of the molecules with the greatest kinetic energy from the liquid to the gaseous state.

The dissolving agent of a solution. Water is the most versatile solvent known.

The sphere of water molecules around a dissolved ion.

The sum of the masses of all the atoms in a molecule; sometimes called molecular weight.

The number of grams of a substance that equals its molecular weight in daltons and contains Avogadro’s number of molecules.

A common measure of solute concentration, referring to the number of moles of solute per liter of solution.

A substance that increases the hydrogen ion concentration of a solution.

A single proton with a charge of 1+. The dissociation of a water molecule (H₂O) leads to the generation of a hydroxide ion (OH^-) and a hydrogen ion (H⁺).

A water molecule that has lost a proton; OH^-.

A water molecule that has an extra proton bound to it; H₃O⁺.

A substance that reduces the hydrogen ion concentration of a solution.

A substance that consists of acid and base forms in a solution and that minimizes changes in pH when extraneous acids or bases are added to the solution.

The study of carbon compounds (organic compounds).

An organic molecule consisting only of carbon and hydrogen.

One of several compounds that have the same molecular formula but differ in the covalent arrangements of their atoms.

One of several compounds that have the same molecular formula and covalent arrangements but differ in the spatial arrangements of their atoms owing to the inflexibility of double bonds.

A specific configuration of atoms commonly attached to the carbon skeletons of organic molecules and usually involved in chemical reactions.

A giant molecule formed by the joining of smaller molecules, usually by a condensation reaction. Polysaccharides, proteins, and nucleic acids are macromolecules.

A reaction in which two molecules become covalently bonded to each other through the loss of a small molecule, usually water, in which case it is also called a dehydration reaction.

A chemical reaction in which two molecules covalently bond to each other with the removal of a water molecule.

A covalent bond formed between two monosaccharides by a dehydration reaction.

A storage polysaccharide in plants, consisting entirely of glucose monomers joined by a glycosidic linkages.

A lipid consisting of three fatty acids linked to one glycerol molecule; also called a triacylglycerol or triglyceride.

A long carbon chain carboxylic acid. Fatty acids vary in length and in the number and location of double bonds; three fatty acids linked to a glycerol molecule form a fat molecule, also known as a triacylglycerol or triglyceride.

A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that are attached to the carbon skeleton.

A fatty acid possessing one or more double bonds between the carbons in the hydrocarbon tail. Such bonding reduces the number of hydrogen atoms attached to the carbon skeleton.

An unsaturated fat containing one or more trans double bonds.

A type of lipid characterized by a carbon skeleton consisting of four rings with various chemical groups attached.

The covalent bond between the carboxyl group on one amino acid and the amino group on another, formed by a dehydration reaction.

The level of protein structure referring to the specific sequence of amino acids.

The localized, repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bond formation between constituents of the backbone.

One form of the secondary structure of proteins in which the polypeptide chain folds back and forth. Two regions of the chain lie parallel to each other and are held together by hydrogen bonds.

Irregular contortions of a protein molecule due to interactions of side chains involved in hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges.

A type of weak chemical bond formed when molecules that do not mix with water coalesce to exclude water.

A strong covalent bond formed when the sulfur of one cysteine monomer bonds to the sulfur of another cysteine monomer.

A technique that depends on the diffraction of an X-ray beam by the individual atoms of a crystallized molecule to study the three-dimensional structure of the molecule.

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses).