|Harmonic oscillator||A system in which a mass is subject to a linear restoring force, like an ideal spring. A harmonic oscillator vibrates at a fixed frequency, independent of amplitude.|
|Heat||As defined in thermodynamics, heat is the energy that flows between two systems as a result of temperature differences (a system contains neither heat nor work, but can produce heat or do work). Heat thus differs from thermal energy.|
|Heat capacity||The ratio of the heat input to the temperature increase in a system. Note that this definition does not imply that a system contains heat, despite the name heat capacity.|
|Helmholtz free energy||The internal energy of a system minus the product of its entropy and temperature; see free energy.|
|Hydrocarbon||A molecule consisting only of H and C.|
|Hydrogen bond||A hydrogen atom covalently bound to an electronegative atom (e.g., nitrogen, oxygen) has a significant positive charge and can form a weak bond to another electronegative atom; this is termed a hydrogen bond.|
|Hydrophobic force||Water molecules are linked by a network of hydrogen bonds. A nonpolar, nonwetting, surface (e.g., wax) cannot form hydrogen bonds. To form their full complement of hydrogen bonds, the nearby water molecules must form a more orderly (hence lower entropy) network. This both increases free energy and causes forces that tend to draw hydrophobic surfaces together across distances of several nanometers.|
Copyright © 1998 by John Wiley & Sons, Inc.