Chapter 16 Liquids and Solids Flashcards
Surface tension (y)
Resistance of the surface of a liquid to an external force because of the attractive forces between molecules. Because of this it resists any increase to its surface area.
Surface tension relasonships
Surface tension decreases with increasing temp because higher temp means greater KE
Relasonship between KE and attractive forces
Greater KE = movement of molecules which decreases the pontential for attractive forces between molecules.
Lower attractive forces —-> surface tension will decrease
Cohesive Forces
Forces between like molecules. Water droplet will stay intact on top of a surface. This phenomenon is observed with water droplets on a recently waxed car.
Adhesive Forces
Forces between unlike molecules. A water droplet will spread out over a surface because the water molecules prefer the surface over each other
Viscosity
Resistance to flow of a liquid and is a result of cohesive forces.
- As temp increases viscosity decreases because of higher kinetic energy
- Large complicated molecules tend to be more viscous because they become entangled more easily.
Vapor Pressure(vp)
Every liquid will have a partial pressure of the gas directly above the liquid, which is called a vapor pressure(vp). Every liquid will have a vapor pressure which will be low. Less than atmospheric pressure
Energy of Evaporation as Hvap, or enthalpy of vaporization.
- change in H vap is an endothermic process which is greater than zero.
Change in H vap = H vap - Hliq >0
Heat is absorbed and enters system
Enthalpy of condensation (Hcond) is less than zero.
Heat is being released by the process in order to allow condensation from gas to liquid state.
Change in Hcond = Hliq - Hvap = - Hvap <0
Vapor Pressure relationships
As temperature increases will the vapor pressure,
Vapor pressure = atmospheric pressure, the liquid will begin to boil = boiling point
Stronger forces = lower vapor pressures
Tips to remember with gas pressure relation
Density of the gas increases as density of liquid decreases
- Surface tension between the phases will approach zero and the interface will disappear
- The density of liquid = gas + surface tension = 0
Substance reached its critical temp and critical pressure = Critical point
Clausius Clapeyron equation
Ln P2/P1 = Hvap / R (1/T1 - 1/T2)
Constants
8.314 J/mol K
- Temperature must be in Kelvin
- Pressure can be any units as long as they are consistent
- Change in H vap can be found in tables given in Kj/mol. All units must be converted to J.
Normal boiling point P =1atm. T= 373K and P = 1atm
Ideal gas law
N = PV/RT
What causes states to change
Deposition: G ——> S
Sublimation S—-> G
Freezing: Liquid —-> solid
Melting : solid —-> liquid
Vaporization: liquid —-> gas
Condensation gas—-> liquid
Sublimination formula
Change in Sublimination = change in H fusion + change in H vaporization
Deposition formula
- Change in H deposition = H vaporization + change in H fusion
Graph order of Physical states Least temp to greater temp
Solid, melting, liquid, boiling, vapor
-With time and increase in temp the physical states change
Isobar
Phase diagram is a line at constant pressue
Isotherm
On the phase diagram is a line at constant temp
Real gas equation
(P + n^2a/(V^2)) (V-nb) = nRT
Intramolecular forces
- Ionic
- Covalent
- Metallic
Energy or strength of intramolecular forces (Kj/mol)
Ionic: (400-4000)
Covalent ( 150-1100)
Metallic (75-1000)
Intermolecular forces
Ion Dipole
H-Bon
Dipole-Dipole
Ion-induced dipole
Dipole-induced Dipole
Dispersion(London)
Energy or Strength (kJ/mol )
Ion-Dipole: 40-600
H-Bond: 10-40
Dipole-Dipole: 5-25
Ion-induced Dipole: 3-15
Dipole-Induced Dipole 2-10
Dispersion(London): 0.05-40
Instaneous dipole
Created in the molecule with a partially negative charge and a partially positive charge. Points from positive to negative.
London force release ship with molar mass of a molecule
London force will also increase as molar mass of a molecule increases.
Polarizability
Is the ability for an atom or molecule to form instanous dipoles and it increases as volumes occupied by electrons increases.
Hydrogen-bonding (H-bonding)
A third common intermolecular force, which is a very strong dipole force that earned it a category of its own.
H-bonding occurs when
H atom is directly bonded to an electronegative element (usually an N,O, or F atom) forming a very strong dipole
0 H-bond actually occurs between the of one molecule and electronegative element of the other.
How do identify the dominant force present.
If yes, the dominant force is ionic
If no, ask if there is an H atom with either an N, O, or F atom.
i. Yes the dominant force is H-bonding
ii. If no, ask if the molecule is asymmetric?
1. If yeast the dominant force is dipole
2. If no, the dominant force is London
Strengths of intermolecular forces ranked greater to weak
Ionic(Strongest)
H-bond
Dipole
London (weakest, but increase as the molecule increases in size
If the force is high then all the following are true
Viscosity is high
Surface tension is high
Boiling point (bp) is high
Vapor pressure (vp) is low
Enthalpy of vaporization (Change in H vaporization) is high.
Five different unit cells along with characteristics
Location of Atom in Unit Cell
Corner
Edge
Face
Center
Number of Atoms in Unit Cell
1/8
1/4
1/2
1
5 types of crystal structures you need to know
Simple cubic :
Body-centered cubic (bcc)
Face-centered cubic (fcc)
Hexagonal-close packed (hcp)
Cubic close packed (ccp)
Density formula
D=m/v
Mass equation
M= (atoms/unit cell) ( mol/6.022e^23 atoms) (grams/mol) = (atoms/unit cell) (Molar Mass/NA)
Common conversions of length
1m =10^10 A
1m= 100cm
1m =10^9
1m = 10^12
Bragg’s Law
N( wavelength) = 2d sin theta
D: is the distance between atom or diffracting planes
Wavelength of the x ray
Theta is the incident angle of the X-rays
N is an integer usually 1
Boiling point definition
