chemistry thermodynammics

Thermodynamics definitions.

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  • Created by: Nora
  • Created on: 22-03-12 20:56

Energy

Enthalpy change -  H

  H=mc  T

- =exothermic

+ =endothermic

 Hf. =heat formation

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Definitions

Law on Conservation of Energy (first law of thermodynamics

Energy can neither be created not destroyed, but only changed from one form to another.

Hess's Law

The enthalpy change involved in a chemical reaction is the same, irrespective of the route by which the reaction takes place, provided that the temperature and pressure are constant.

Enthalpy(heat)change of reaction

This is the enthalpy change that occurs for the amounts specified in the equation at 298K and 100KPa pressure, with the substances in their physical states normal under these conditions.

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Enthalpy(heat) change of formation

This is the enthalpy change that occurs in the formation of 1 mole of a compound from its elements at 298K and 100KPa pressure, with the substances in their physical states normal under these conditions.

Enthalpy(heat) change of combustion

This is the enthalpy change produced when 1 mole of a compound is completely burnt in excess oxygen at 298K and 100KPa pressure, with the substances in their physical states normal under these conditions.

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Enthalpy(heat) change of hydrogenation

This is the enthalpy change that occurs, when 1 mole of an unsaturated compound is converted to 1 mole of a saturated compound by reaction with hydrogen, at 298K and 100KPa pressure, with the substances in their physical states normal under these conditions.

Bond dissociation enthalpy

The standard molar bond dissociation enthalpy is the enthalpy change, when one mole of bonds of the same type, in gaseous molecules under standard conditions is broken, producing free radicals.

Mean bond enthlpy or Bond enthalpy term E(A-B)

This is the enthalpy change required to break a 1 mole of a specific covalent bond. The value can vary depending on the environment in which the particular bond is found, so an average or 'mean' value is used.

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