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Enthalpy / Entropy (Enthalpy definitions (The Standard enthalpy change of…
Enthalpy / Entropy
Enthalpy definitions
- The Standard enthalpy change of atomisation
- the enthalpy change that takes place for the formation of one mole of gaseous atoms from the elements in its standard state under standard condition
- (Endothemic)
- Lattice enthalpy
- the measure of the strength of ionic boning in a giant ionic lattice.
- the enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions
- (Exothermic)
- The enthalpy change of neutralisation
- the enthalpy change that accompanies the reaction of an acid by a base to form one mole of water under standard conditions with its reactants and products in standard state
- The enthalpy change of Combustion
- the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions with the reactants and products in standard state
- The enthalpy change of formation
- the enthalpy change that takes place when one mole of a compound is formed from its element under standard condition, with its reactants and products in standard state
- The Standard enthalpy change of Reaction
- the enthalpy change that accompanies a reaction in molar quantities shown in the equation under standard condition, with the reactants and product in standard state
- First ionisation energy
- the enthlapy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous +1 ions
- (Endothermic)
- First electron affinity
- the enthalpy change that accompanies when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous -1 ions
- (Exothermic)
- all electron affinities after the first are endothermic
- Enthalpy change of solution
- the enthalpy change that takes place when one mole of a solute is dissolved in a solvent (water)
- Enthalpy change of hydration
- the enthalpy change that takes place when gaseous ions are dissolved in water to form one mole of aqueous ions
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Average Bond enthalpy
energy needed to break one mole of a specified type of bond in a gaseous molecule
- bond enthalpies are always endothermic
Hess' law
if a reaction can take place by routes and the start and finish conditions are the same, the total enthalpy change is the same for each route.
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Exothermic change - from system to surrounding
- delta H is negative
Endothermic change - from surrounding to system
q = mc(change in)T
q = heat energy (J)
m = mass of the surrounding (m)
c = specific heat capacity of the surrounding (J g^-1 K^-1
T = temperature
Reasons why Experimental is different to Data book
- heat loss in surrounding like air
- imcomplete combustion
- evaporation
- not standard solution