Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 6 : Properties of Matters - Coggle Diagram
Chapter 6 : Properties of Matters
Liquid
Properties of Liquid
Viscosity
Viscosity is a measure of the resistance to
flow (measured in units called poise pronounced 'pwahz')
~Viscosity depends on any factor that can
influence the ease with which molecules slip past each other.
~Liquids tend to become more viscous as
the size of molecules become larger, as the amount of intermolecular bonding increases and the temperature decreases.
The viscosity of water at room temperature
is roughly 1 centipoise, or 1 cP (the viscosity of water decreases from 1.77 cP at 0oC to 0.28 cP at 100oC)
Surface Tension
The force that controls the shape of the
liquid is called the surface tension
~Below the surface of the liquid, the force
between molecules is the same in all directions, but at the surface the force of attraction pulls the molecules into the liquid
As a result, the liquid takes on the shape of a
sphere (a shape that has the smallest surface area)
Vapour Pressure
The vapor pressure of a liquid is the pressure
of the vapor (gas) above the liquid at a given temperature
~A liquid open to the air will (over time)
evaporate completely; however in a closed container some of the evaporated molecules
may return to the liquid
~Over time an equilibrium will be established
(the rate at which molecules evaporate is equal to the rate at which molecules return
to the liquid)The gas pressure under this equilibrium condition is called the vapor
pressure
~The boiling points of most liquids are
proportional to the vapor pressure
Colligative Properties
Boiling point elevation
The boiling point of a solution containing
nonvolatile solute is greater than the boiling point of the pure solvent
The boiling point of a liquid is the temperature at which the vapor pressure of that liquid equals 1.0 atm)
The change in boiling point is given by the van't Hoff equation for boiling point:
ΔTb = Kb x m where,
ΔTb = boiling pt of solution - boiling pt of solvent
Kb is the boiling pt elevation constant
m is the molality of the solution
Freezing point depression
The freezing point of a solution containing nonvolatile solute is lower than the boiling point of the pure solvent.
The change in freezing point is given by the van't Hoff equation for freezing point:
ΔTf = - Kf x m
where,
ΔTf = freezing pt of solution - freezing pt of solvent
Kf is the freezing pt depression constant
m is the molality of the solution
(Note the negative sign in the equation)
Vapor pressure lowering
The vapor pressure of a solution containing nonvolatile solute is lower than the pure solvent.
The solvent molecules will have a lower probability to escape the solution than the pure solvent, resulting in lower rate of vapor formation, thus lower vapor pressure
The Raoult's Law describes the vapor pressure lowering:
ΔP solution = Xsolute Po
where, ΔP solution is the vapor pressure difference
Xsolute is the mole fraction of the solute
Po is the vapor pressure of the pure solvent
Osmotic pressure
Osmosis
~Osmosis is the selective passage of solvent
molecules through a porous membrane from a dilute solution to a more concentrated one.
~A semipermeable membrane allows the passage of solvent molecules but blocks the
passage of solute molecules
The equation relating the osmotic pressure
of a solution to its concentration is
π= M R T
where, π is osmotic pressure
R is the gas constant
T is the absolute temperature
M is the molarity of the solution
The osmotic pressure is the back pressure (or
opposing pressure) needed to prevent osmosis
~Osmosis refers to the flow of solvent
molecules past a semi permeable membrane (that stops the flow of solute molecules)
~The following figure shows a typical setup for
measuring the osmotic pressure of a solution
Gas
Properties of Gases
Three variables are used to measure gases:
pressure, volume, and temperature
~Volume of a gas is equal to the volume of
the container that holds the gas
~Temperature is the heat energy due to the
motion of the gas particles
~Pressure is force per area (standard SI unit
is pascal, Pa)
Pressure is the result of collisions between
the gas particles and the collisions betweenparticles and the walls of the container that
holds the gas
Gas Law
Describe the changes in physical properties
of gases under specific conditions
Boyle's Law
The volume of a given mass of a gas is inversely
proportional to pressure at constant temperature
V∝1/p
Comparing two conditions, initial (1) and final (2),
the equation for Boyles Law is P1V1 = P2V2
Charles's Law
The volume of a given mass of a gas isproportional to absolute temperature at
constant pressure
V ∝T
Comparing two conditions, initial (1) and final (2), the equation for Charles Law is V1/T1=V2/T2
Avogadro's Law
The volumes of gases are proportional to the number of atoms or molecules
V ∝ n {at STP or standard temperature and
pressure, 273K (0oC) and 1 atm}
1 mole gas = 22.4 L at STP
V/n=k (k= proportionality constant)
Ideal gas Equation
The Ideal Gas Law is derived by combining Boyle’s Law, Charle’s Law and Avogadro’s
Law
A gas which obeys the Ideal Gas Law iscalled an ideal gas (perfect gas)
The Ideal Gas Law equation is PV=nRT
P = pressure in atm
V = volume
T = temperature in Kelvin
n = number of moles
R is the gas constant = 0.0821 L atm mol-1 K-1
The Ideal Gas Law can be used to determine density
(p= mass per volume) or molar mass (g mole-1) of a gas
Dalton's Law of Partial Pressure
The sum of the partial pressures of the gases in a mixture is the total pressure of the gas:
Ptot = PA + PB + PC + ...
Ptot = total pressure
PA, PB, PC …. are partial pressures
The Dalton' law is generally used for
determining the actual pressure of a gascollected by the water displacement method:
PH2O vapor + Pdry gas = Ptot (measured)
The partial pressures of gases eg A and B in a mixture can be also calculated as follows:
PA = nA (RT/ V) or PA = XA x Ptot
PB = nB (RT/V) or PB = XB x Ptot
XA = mole fraction of A = nA /ntot
XB = mole fraction of B = nB /ntot
Graham's Law of Effusion (Diffusion)
Diffusion : Rate at which two gases mix
Effusion : Rate at which a gas moves through
a small hole
The rate of effusion of a gas is inversely
proportional to the square root of its density
Comparing effusion of two gases, A and B
Since density (p) is proportional to molecular mass (M), therefore, density can be replaced
by M
Equation for Graham’s Law
Kinetic Theory of Gases
The Kinetic Theory of Gases is based on the following assumptions and describes the properties of an ideal gas:
~The volumes of gas particles are negligible (very small)
.This explains why gases are compressible
~Intermolecular forces do not exist between gas particles
This explains why gas particles do not influence each other and fills up a container
~Gas particles move in random motions and collide without energy loss (elastic collisions)This explains why the gas particles collide with one another and the walls of a container without energy lose
~The kinetic energy of a gas is directly proportional to absolute temperature.This explains why when gas is heated the particles move faster
Equations involving Kinetic Energy (KE) and
velocity (u) of gas molecules are given as follows:
KE = 1/2mu2 = 3/2kT
Where, R = gas constant, M = molecular
mass,
NA = Avogadro's number
k = R/NA
m = M/NA
The root mean square velocity, u =
Solid
Properties of Solid
Types of Solids
Crystalline solids
The atoms, molecules or ions are arranged in
a regular pattern (an ordered three-dimensional arrangement)
~They exhibit anisotropic properties
(measurements of mechanical / electrical properties depend on direction)
~They have sharp (specific) melting points
Types of Crystalline Solids
Covalent crystals
~A network of covalently bonded atoms forming
a gigantic molecule
~Have high melting points and tend to be hard
(strong covalent bonds)
~Non conductors (eg Diamond (C), quartz, SiO2)
Metallic crystals
~Consist of positive metal ions
~Melting points and hardness depend on thenuclear charge and electrons
~Conductors (eg Cu, Hg, Na)
Molecular crystals
~Consist of uncharged atoms/molecules
~Have low melting points and tend to be soft (reflecting weak intermolecular forces)
~Non conductors (eg water, solid CO2)
Types and Examples of Crystalline Solids
Ionic crystals
~Consist of positive and negative ions alternately arranged
~Have high melting points, tend to be hard or brittle (reflecting strong electrostatic forces)
~Conduct electricity in the molten or soluble state (eg NaCl, CaCl2)
Amorphous solids
~Particles have no regular pattern of
arrangement (consist of intertwined chainlike particles/molecules)
~Melt over a range of temperatures(eg Rubber, glass, sulfur)
Unit Cells, Crystal Lattices and Crystal
System
~A unit cell is the smallest basic unit of a
crystal that can be repeated in three dimensions throughout the crystal lattice
~A crystal lattice is the repeating pattern of particles in a crystalline solid
A crystal system is a method of classifying
crystalline substances on the basis of their unit cells
There are 7 crystal systems (with all points at
the corners only)
1.Cubic
2.Tetragonal
3.Orthorhombic
4.Monoclinic
5.Triclinic
6.Hexagonal
7.Rhombohedral
The cubic system
The cubic system is made up of three types
of lattice arrangements
Body-centered cubic lattice (has a lattice
point at each corner and an additional lattice point in the center of the unit cell)
Face-centered cubic lattice (has a lattice
point at each corner and an additional atom at each of its six faces)
Simple cubic lattice (has a lattice point at
each corner of the unit cell)
Number of units in a unit cell
The number of units (atoms, ions or molecules) in a unit cell can be calculated by applying the following rules:
~A corner unit is shared by 8 unit cells = 1/8 unit per cell
~A face unit is shared by 2 unit cells= ½ units per cell
~An edge unit (at the edge of the unit cell) is shared by 4 unit cells = ¼ unit per cell
~A body unit (in the center of the unit cell) is unique to 1 unit cell = 1 unit per cell
Atomic radius and Density
The radius of an atom can be calculated
from the crystal structure of a substance using data obtained from a method known as
X-ray analysis
