Lecture 17 Flashcards
The amount of heat needed to melt one mole of a solid is called
the heat of fusion (ΔHfus)
Crystallization amount of energy process
ΔHcrystal = -ΔHfus
Vaporization amount of energy compared to fusion
ΔHvap > ΔHfus
Heat of fusion of water plus melting point
H20-melting point:( 0C ), heat of fusion: 6.02 kJ/Mol
Heat of fusion of isopropyl alcohol
C3H7OH- melting point: ( -89.5 ), heat of fusion: 5.37
heat of fusion of acetone
C3H6O -melting point (-94.8 ), heat of fusion: 5.69
Heat of fusion of Diethyl ether
C3H10O melting point: (- 116.9 ), heat of fusion: 7.27
Stronger intermolecular forces =
higher boiling points, melting points, and heat of vaporization; they also have lower vapor pressures.
Miscible
Liquids that do not separate, no matter what the proportions.
Dispersion forces
London forces or instantaneous dipoles.
Caused by distortions in the electron cloud of one molecule inducing distortion in the electron cloud on another.
The temporary dipoles lead to attractions between molecules
Strength of dispersion force compared to size of molecule
Strength of the dispersion force gets larger with larger molecules
size of molecule (Mm vs. boiling point)
smaller the gas, the lower the boiling point
Polar molecules
oppositely charged atoms (h20)
Non polar molecules
Equally charged, generally dissolved in non polar. CO2.
covalent bond
2 non metals bonded, electron sharing
Ionic
Electron transfer. Metal + non metal. Cations plus anions. Metal + polyatomic compound.
Dipole to dipole attraction
Polar molecules have permanent dipole (a+ end and a- end and + end always attaches to - end of another)
Polarity and dipole to dipole attraction
The bigger the dipole size, the higher the boiling point. Polar molecules
Immiscible liquids
DO NOT mix because they are more attracted to their own kind than the other (oil and water example-polar and non polar)
Hydrogen bonding (HF, OH, NH groups) bond strength and other features
STRONG bonds. High boiling, melting, and solubility in water. NOT a chemical bond.
In order of strongest to weakest bonds (forces)
Hydrogen bonds> Dipole to Dipole force > Dispersion force (all have dispersion force)
Molecular solids (crystalline solids)
Composite units are molecules. Low melting
Ionic solids
Composite units are formula units (cations and anions). High melting. (NACL)
Atomic solids
Composite units are atoms. Variable melting.
