Chem5

Enthalpy of formation

The energy transfer when 1 mole of the compound is formed from its constituent elements under standard conditions, all reactants and products being in their standard states.

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Enthalpy of atomisation

The enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard state.

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Bond dissociation enthalpy

Standard molar enthalpy change when one mole of a covalent bond is broken into two gaseous atoms(or free radicals)

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First ionisation enthalpy

Enthalpy change required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous ions with a +1 charge

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Second ionisation enthalpy

The enthalpy change to remove one mole of gaseous 1+ ions to produce one mole of gaseous 2+ ions.

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First electron affinity

enthalpy change when one mole of gaseous atoms gain 1 mole of electrons to form one mole of gaseous ions with a -1 charge.

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Second electron affinity

Enthalpy change when one mole of gaseous 1-ions gains one electron per ion to produce gaseous 2-ions.

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Enthalpy of lattice formation

standard enthalpy change when 1 mole of an ionic crystal lattic is formed from its constituent ions in gaseous form.

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Enthalpyof lattice dissociation

Standard enthalpy change when 1 mole of an ionic crystal is seperated into its constituent ions in gaseous form.

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Enthalpy of Hydration

Enthalpy change when 1 mole of gaseous ions becomes aqueous.

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Enthalpy of solution

The standard enthalpy change when 1 mole of an ionic solid dissolves in an large enough amount of water to ensure that the dissolved ions are well seperated and do not interact with one another.

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State and explain the trend in lattice enthalpies of ionic compounds

larger ions give smaller lattice enthalpies. Because as the ions are larger the charges become further apart and so have weaker attractive forces between them.

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Why does the lattice enthalpy increase with size of charge?

the bigger the charge of the ion, the greater the attraction betwen the ions so the stronger the lattice enthalpy.

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Perfect ionic model

Ions are 100% ionic,spherical and the attractions are purely electrostatic.

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When is there a tendancy towards covalent character in ionic substances?

positive ion is small. Positive ion has multiple charges. The negative ion is large. The negative ion has multiple negative charges.

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State and explain the effect on the born haber value compared to the theoretical value if the compound has some covalent charcteristics.

Born haber value would be larger than theoretical. compound tends towards giant covalent so the lattic is stronger than if it was 100% ionic.

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what are the units of entropy

JK-1mol-1

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state conditions in which a significant increase in entropy will occur.

Change of state or significant increase in number of molecules between products and reactants.

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what two conditions would mean a reaction is always feasable

increasing entropy and exothermic.

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