the enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions under std. conditions
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Why is lattice energy always exothermic?
Because it is the bonding together of ions, not the separation of ions.
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enthalpy change of atomisation
the enthalpy change when 1 mole of gaseous atoms is formed from its element under std. conditions
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Are values of en. change of at. positive or negative, and why?
Positive; energy must be supplied to break the bonds holding the atoms in the element together.
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electron affinity
the enthalpy change when 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions under std. conditions
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Is the en. change for electron affinities positive or negative?
First e.a. is negative. Second e.a. is always positive, so are third e.a.
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What are the factors affecting the lattice energy?
size & charge of the ion
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How does ion size affect latt. energy?
As size of the ion increases, latt. energy becomes less exothermic.
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How does ion charge affect latt. energy?
Latt. energy becomes more exothermic as ionic charge increases.
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What is ion polarisation?
It is the distortion of the electron cloud on anion by a neighbouring cation. .
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What is polarising power?
the ability of a cation to attract electrons and distort an anion
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On what does the degree of polarisation depend on?
the charge density of the cation & the ease with which the anion can be polarised
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An anion is more likely to be polarised if...
the cation is small, the cation has a charge of 2+/3+, the anion is large & the anion has a charge of 2-/3-
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What is the thermal stability pattern of Group 2 carbonates and nitrates?
increases down the group
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Why do the thermal stabilities of carbonates and nitrates increase down Group 2?
The ionic radius in. down the group. The smaller the ionic radius of the cation, the better it is at polarising. The charge density dec. down the group. So the degree of polarisation dec. down the group, and the easier it to weaken the bonds by heat.
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enthalpy change of solution
the energy abosrbed/released when 1 mole of an ionic solid dissolves in sufficient water to form a very dilute solution
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What should the en. change of solution value be for a compound to be soluble?
negative or a small positive value
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enthalpy change of hydration
the enthalpy change when 1 mole of a specified gaseous ion dissolves in sufficient water to form a very dilute solution
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Are values of en. change of hyd. endothermic or exothermic?
exothermic
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When are values of en. change of hyd. more exothermic?
For ions with the same charge but smaller ionic radii & for ions with the same radii but a larger charge.
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calculating en. changes in solution
lattice en. + solution en. = hydration en.
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What is the trend in solubility in water of Group 2 sulfates?
decreases down the group
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What is the relationship between solubility of Group 2 sulfates and metal ion radii?
The solubility deceases as the radius of the metal ion increases.
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What is the change in hyd. en. down Group 2 sulfates?
decreases down the group
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What is the change in latt. energy down Group 2 sulfates?
decreases down the group
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Other cards in this set
Card 2
Front
Why is lattice energy always exothermic?
Back
Because it is the bonding together of ions, not the separation of ions.
Card 3
Front
enthalpy change of atomisation
Back
Card 4
Front
Are values of en. change of at. positive or negative, and why?
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