Thermodynamics 4 Flashcards
Define enthalpy of fusion
The change from one mole of a solid to 1 mole of a liquid is known as enthalpy of fusion.
Define enthalpy of vaporization.
the change from one mole of a liquid to 1 mole of a gas is known as enthalpy of vaporization.
define enthalpy of sublimation.
the change from one mall of a gas to one mall of a solid is known as enthalpy of sublimation.
define standard enthalpy formation.
The standard enthalpy change for formation of one mole of a compound from its elements in the most stable states of Aggregation also known as reference states is called standard molar enthalpy of formation.
eg: - H2 + 1/2 O2 –> H2O
delta H=-285.8kJ/mol
under what conditions standard molar enthalpy of formation is not applicable?
- If not 1 mole of product is not formed.
- If there are no elements in the reactants side of the equation.
Hess law of constant heat sublimation
if a reaction takes place in several steps then the standard reaction enthalpy is the sum of the standard enthalpies of the intermediate reactions into which the overall reaction may be divided at the same temperature.
Define standard enthalpy of combustion.
It is defined as the enthalpy change per mole of a substance when it undergoes combustion when all the reactants and products are in the standard state.
Eg: - C6H12O6 + ^o2 –> 6CO2 + 6H2O
delta c H ° = -2802 kJ/mol
define Enthalpy of atomization
It is the enthalpy change on the breaking one mole of bond completely to obtain atoms in the gaseous state.
Eg: - H2(g) –> H(g) + H (g)
delta a H ° = 435 kJ/mol
Define bond dissociation enthalpy.
it is a change in the enthalpy when one mole of covalent bond of the gaseous covalent compound is broken to form products in the gaseous phase.
Eg: - H2(g) –> H(g) + H(g)
How is the standard enthalpy of reaction related to the bond enthalpy of reactants and the products in the gaseous phase.
∆rH° = Σ bond enthalpies of reactants - Σbond enthalpies of products
