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Chapter 11 - Coggle Diagram
Chapter 11
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Liquid solutions
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[solutions of a solid or liquid into a liquid solvent]:
- Salt + Water
- Polar Solute + Polar Solvent
- Alcohol + Water
- Apolar solute + Apolar solvent
Short chain alcohols dissolves very well in water (both polar), but for long chain the idrophobic group R is an obstacle. (The latter are more soluble in Hexane, which is apolar)
CaCl2 + H2O is exothermic (anti-freezing)
NH4NO3 +H2O is endothermic (ice pack)
NaCl + H2O is endothermic
NaOH + H2O is exothermic
Gibbs free Energy change ΔG
is a state function related to potential energy of a chemical/phisical process
- ΔG < 0 (increase of Universe entropy ΔS increse)
- ΔG > 0 process is not spontaneous
- ΔG = 0 process is at equilibrium
Gibbs-Helmholtz equation
ΔG = ΔH - T*ΔS
[ΔS change in entropy = Heat at constant pressure - disorder in a mixture]
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ΔG < 0
the solution froms spontaneously:
- ΔS > 0 increase the molecular disorder
- ΔH = 0 it is an ideal solution (ΔG=-TΔS)
- ΔH < 0 exothermic (ΔG = -ΔH-TΔS <<0)
- ΔH endothermic |ΔH|<|TΔS|
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Solutions are: Homogeneous mixtures composed by Solvent (the major component) Solute (the other components)
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Water as a Sovent causes Hydratation:
this means ions in water are never alone, they're always surrounded by H2O molecules (called Hydratation shells) (8 - octahedral shape to minimize repulsion)
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Electrolytes and non-Electrolytes
Electrolyte is a solute that forms a conductor solution.
- Strong electrolytes (completely dissociated) α = 1
- Weak electrolytes (partially dissciated) 0<α<1
[α = num. diss.molecules / tot. diss. molecules]
Non electrolytes do not fors ions so are not conductors
[sugar dissolves in H2O but is not a conductor]
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Colligative's property of solutions
[do not depends on number of particles]
vapour pressure depression:
ΔP = P0(sv) - P(sv) = X(so) * P0(sv)
[non-volatile solute makes the vapour pressure of the solvent decrease]
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The Raoult's Law
ΔP = P0(sv) - P(sv) = Xso P0(sv)
P(sv) = X(sv) P0(sv)
This is true for ideal solutions ΔHsn = 0
for electrolytes one need the Van't Hoff factor "i"
i = [1 + (v - 1) * α]
ΔP = (n(so) * i(so) / n(so) * i(so) + n(sv)) * P0(sv)
Deviation from Ideal Solutions (ΔH(sn) = 0)
- solute - solvent interactions are weak => positive deviation (evaporates easily)
- solute - solvent interactions are strong => negative deviation (evaporates difficultly)
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Solid solution are called alloys can be: substitutional alloy (Zn + Cu = Brass) or interstitial alloy (C + Fe = carbon Steel)
Solubilityis the max amount of solute that can be dissolved in a solvent at a given temperature.
[usually are more soluble at high T (but not CaCO3)]