Thermodynamics and Intermolecular Forces Definitions

  • Created by: E.H13
  • Created on: 23-05-20 20:41
Helmholtz Free Energy. The maximum work accompanying a process. Leftover from the internal energy of the system, after you've taken out the energy stored as random thermal motion (as this can't be used)
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Gibbs free energy. The maximum non-expansion work accompanying a process, measured at constant pressure.
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Three things Gibbs depends on
Temperature, pressure and amount of species present.
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Homogeneous system
Each intensive macroscopic property is constant throughout the system
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A homogeneous part of a system
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Phase Transition
Spontaneous conversion of one phase to another (e.g. boiling, melting, sublimation)
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Degrees of Freedom
The number of intensive variables needed to specify the intensive state of the system
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Vapour pressure
Pressure of the vapour in equilibrium with the condensed substance. Variation shown by either the L-V or S-V boundary.
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Boiling Temperature
The temperature at which the vapour pressure of a liquid is equal to the external pressure
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Normal boiling point
1 atm
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Standard boiling point
1 bar
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Critical point
Vapour pressure equal to the pressure of the liquid in a closed, heated and rigid vessel.
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Supercritical fluid
The point at which 2 phases disappear and become a single phase
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Melting point
The temperature at which the liquid and solid phases co-exist (aka the freezing temperature)
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Triple Point
A set of conditions resulting in the 3 phases co-existing in equilibrium. This cannot be controlled or adjusted.
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Lower Critical Solution Temperature (LCST)
The temperature below which mixing occurs.
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Upper Critical Solution Temperature (UCST)
The maximum temperature where increasing the temperature will flip the sign of d(mix)G
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A point charge (e.g. Na+ or Cl-)
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An asymmetric charge distribution within a molecule with no nett charge
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Monopole moment
The charge of the atom/molecule
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Dipole moment
A vector. Different local charge depends on where in the molecule it is. The magnitude is the product of the charge and the distance between the charge centres.
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Electrostatic Interactions
Interactions between chargd atomic or molecular species or between asymmetric charge distributions in neutral molecules
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A monopole or higher multipole causing polarisation of neighborliness atoms/molecules and induced multipoles
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Induction Energy
The attractive interaction between the original multipole and the induced multipole
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Attractive interactions between instantaneous dipoles arising from fluctuating charge distributions. Only exist for a short amount of time
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Hydrogen bonding
Hydrogen atom covalently bound to one electronegative atom, interacting with a second electronegative atom in the form X-H --- Y
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Van der Waals forces
Term used to cover electrostatic, induction and dispersion interactions between discrete neutral particles
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Limit of Compressibility
Repulsive interactions from the overlap of electron densities which dominate at short range, preventing the matter getting closer.
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Dynamic electron correlation
Fluctuations in electron densities giving rise to instantaneous electronic dipoles, which in turn induce dipoles
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Gibbs free energy. The maximum non-expansion work accompanying a process, measured at constant pressure.

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Three things Gibbs depends on


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Homogeneous system


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