Energy changes in solution

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  • Created by: J.E.C.
  • Created on: 01-05-14 15:28
When ions in soltuion become hydrated, this is a __ process?
Exothermic
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Define lattice enthalpy?
Enthalpy change when one mole of solid is formed by the coming together of the separate ions.
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All lattice enthalpies are large __values?
Negative
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Forming an ionic lattie from gaseous ions is an __ process, so the value for ΔHLE is always ___? The stronger the ionic bonding in the lattice, the more __ the ΔHLE?
Exothermic, negative. Negative
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Lattice enthalpies become more negative when the ionic charge __ and the ionic radius __?
Increases, decreases
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Ions with a higher charge attract each other __ strongly or if they are closer together?
More
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Substances with large negative lattice enthalpies are usually...?
Insoluble
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When a substance breaks up the enrgy needed corresponds to...?
The reverse of the LE
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What is the effect of water molecules on ions during hydration?
The polar water molecules act as tiny dipoles, these are attracted to the charges on the ions. The positive ion sbecome surrounded by water molecules with the negative end of the dipole facing them.
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The ions in solution are said to be __ because they have __ __ bound to them?
Hydarated, water molecules
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When hydrated ions crystallise out of solution...?
The strongly bound water molecules crystallise with them to give hydrated crystals.
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The higher the charge density of the the ion the more...?
Water molecules it attracts and the bigger it becomes.
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When bonds form between ions and water molecules, what is released and what is the effect of this?
Energy - may supply enough energy to pull ions out of the lattice
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When ions dissolve in water, some of the water molecules must be __ ___ - this process requires energy as well?
pulled apart
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The strength of attraction between ions and water molecules is measured by the enthalpy of hydration, which is defined as...?
The enthalpy change for the formation of a solution of ions from 1 mole of gaseous ions.
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Enthalpies of hydration are always __? The greater the __ and the smaller the __ the more negative the ΔHhyd value is?
Negative. Charge, radius
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When considering solvents other than water, we use the __ value?
Enthalpy of solvation ΔHsolv
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The hydration of ions favours __ and helps to supply the energy needed to separate...?
Dissolving, the ions from the lattice
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ΔHsol =
ΔHhyd (cation) + ΔHhyd(anion) - ΔHLE
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ΔHhyd is always __ because it is an __ process?
Negative, exothermic
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For a solution in which the hydration provides slightly more energy than is needed to break up the lattice - this type of solute therefore normally...?
Dissolves
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Where the hydration of ions does not provide as much energy as is needed to break up the lattice, the solute usually...?
Does not dissolve
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An increase in entropy, favours...?
Dissolving
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If the enthalpy change of solution valuse is large and positive, the solute...?
Is not likely to dissolve
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Even though CaCO3 has a small negative ΔHsol value, it is insoluble, explain why in terms of entropy?
Overall there is a large entropy decrease because the solute becomes more 'disordered' but the solvent becomes more ordered as water molecules cluster around the doubly charged ions.
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Often substances are not soluble in non polar solvents because...? There would be a large, positve __value indicating it would not be able to dissolve?
There are no regions of slight positive and negative charge - unable to interact strongly with ions. ΔHsol.
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Other cards in this set

Card 2

Front

Define lattice enthalpy?

Back

Enthalpy change when one mole of solid is formed by the coming together of the separate ions.

Card 3

Front

All lattice enthalpies are large __values?

Back

Preview of the front of card 3

Card 4

Front

Forming an ionic lattie from gaseous ions is an __ process, so the value for ΔHLE is always ___? The stronger the ionic bonding in the lattice, the more __ the ΔHLE?

Back

Preview of the front of card 4

Card 5

Front

Lattice enthalpies become more negative when the ionic charge __ and the ionic radius __?

Back

Preview of the front of card 5
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