Oceans - Energy changes and solutions
13 important questions on Oceans - Energy changes and solutions
Why would you expect NaCl to be soluble in liquid ammonia?
- ions form ion dipole bonds with ammonia
- bonds formed compensate for broken hydrogen bonds
- lattice enthalpy/ attractions between ions in NaCl
What 3 things does an exothermic reaction mean?
- more -ve
- dissolves
- spontaneous
The greater the enthalpy change of hydration the...
- stronger the ion dipole attractions
- the greater number of water molecules surrounding the ion
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What can be said about enthalpy change of hydration and lattice energy?
They are always negative because they involve the formation of bonds
What does the ionic radius depend on?
- the nuclear charge (atom no.) = the bigger the charge, the smaller the ion
- the no. of full energy levels = the more energy levels the bigger the ion
What happens when enthalpy change of solution is large and positive?
The solid will not dissolve even though the entropy change will be favourable as too much energy is needed. This is always the case with ionic solutes in non-polar solvents, -*delta H*solv is tiny because there is little attraction between the ions and solvent.
Put the following ionic compounds in order of lattice enthalpy (on formation) from least to most negative: LiF, KF, CaO, CaF2
KF, LiF, CaF2, CaO
Put the following ions in order of enthalpy of hydration from least to most negative: Al^3+, Na^+, Mg^2+, Ca^2+, K+
K^+, Na^+, Ca^2+, Mg^2+, Al^3+
Is silver (I) iodide soluble in water under standard conditions? (look at p.65 Q5(b) revision textbook)
Insoluble -background-color enthalpy change of solution is too endothermic
Thallium (I) bromide is insoluble in water. The main reason for this is the small size of the -ve hydration hydration enthalpy of the Tl+ ion. Give two reasons why this value is small.
- large size
- small charge
Name the interaction between the sodium ions and water molecules.
Ion dipole interaction.
Explain why calcium ions are strongly hydrated in solution and how this effects the entropy change of solution.
Calcium ions are small and highly charged meaning they attract a lot of water molecules. This means the ions are more organised and so have a lower entropy.
Which enthalpy change in a Born-Haber cycle is the best measure of the stability of the compound concerned?
Enthalpy change of formation
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