Transcript Chapter 10

Chapter 10
States of Matter
The Kinetic-Molecular Theory
• Particles of Matter are in a continual state
of motion
KM Theory and Gases
• Ideal Gas: a hypothetical gas that perfectly fits
all assumptions of the km theory
• Five Assumptions:
– Gases consist of large numbers of tiny particles that
are far apart relative to their size
– Collisions between gas particles and between
particles and container walls are elastic collisions
• A collision in which there is no net loss of kinetic energy
• KE transferred between two particles during collisions.
However the total ke of two particles remains same as long
as temperature is a constant
Assumptions continued
– Gas particles are in continuous, rapid, random
motion. They therefore possess kinetic energy, which
is energy of motion
– There are no forces of attraction between particles
– The temperature of a gas depends on the average ke
of the particles of the gas
KE= ½ mv2
KE theory and Nature of Gas
• KE theory only applies to ideal gas
• If temp is not too low or pressure too high,
many gases act ideal
• Theory accounts for physical properties
– Expansion
– Fluidity
– Low density
– Compressibility
– Diffusion and effusion
Deviations of Real Gas from Ideal
• A real gas is one that does not behave
completely according to the assumptions
of the KM theory
• At high pressure and low temperature, gas
particles can not overcome forces of
attraction
• Polar gases deviate from ideal more that
nonpolar
Liquid and KM theory
• Particles in continual state of motion,
however, are closer together that in gas
• Intermolecular forces cause for attractions
(dipole-dipole, London Dispersion, and
Hydrogen Bonding)
• Liquids have a lower fluidity than that of
gases (most flow downhill due to gravity)
Physical Prop of Liquid
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Relatively high density (compared to gas)
Relative incompressibility
Ability to diffuse
Have surface tension
– Forces pull liquid surface together, decreasing
surface area
– Capillary action caused by the surface of
liquid to the surface of a solid---cause of
meniscus
• Evaporation and boiling
– Vaporization: change from liq to gas
– Evaporation: process by which particles
escape the surface of liquid without boiling
• Formation of solids
– Freezing: the physical change from liq to
solid by removal of thermal energy
– Also called solidification
Solids and Kinetic Molecular theory
• Particles closely packed, intermolecular
forces at the highest
• Forces hold particles in relatively fixed
positions—defn. shape
• Two types of solids
– Crystalline: consist of crystals (geometric
patterns)
– Amorphous: one in which the particles are
arranged randomly
• Theory responsible for solid properties of
– Definite shape and volume
– Definite melting point
• Melting is the physical change of a solid to a liquid by the
addition of energy as heat
• Supercooled: substances retain liq properties even at
temperatures at which they appear solid (glass and plastics
are amorphous solids that have no defn. melting point)
– High density and incompressibility
– Low rate of diffusion
Energy Changes
• Every chemical change involves a loss or gain of
energy
• Most usually energy in form of heat
• The amount of heat transfer is measured in
calories (cal) or joules (j)
• 1 j = .239 cal
or 1 cal = 4.184 j
• Temperature is the condition of a body
which determines the transfer of heat to or
from other bodies. It is an indication of the
average kinetic energy of the particles of
which that body is made.
• Heat energy applied to a body may produce one
of two effects in the body
– It may raise the temp
– It may bring about a change of state of that body
• The amount of heat needed to change a substance from a
solid to a liquid is called its heat of fusion
• The amount of heat needed to change a substance from
liquid to gas is called heat of vaporization
• Heat absorbed or released during a chemical change is
known as the heat of reaction. The heat of reaction is
usually expressed in units of kcal/mol
Heat of fusion (Hf)
• Most calc. are going to use
Q=m x Cp x ▲T
Q= quantity of heat
M=mass
Cp= specific heat (The amount of heat, measured in calories,
required to raise the temperature of one gram of a substance by one
Celsius degree. )
▲T=change in temperature
Hf= Q/m
Hf=heat of fusion usually in cal/g or j/g
Q=quantity of heat
M=mass
Heat of vaporization Hv
• Hv=Q/m
Hv=heat of vaporization
Q=quantity of heat
M=mass
Example
• How much heat is released when 52.5 g of
water cools from 67.5 to 23.3 Celsius?
The specific heat of water is 1.00cal/Cg
Q=m x Cp x ▲T
Q=52.5g x 1.00 cal./Cg x (67.523.3)
Q=2330 cal or 2.33 Cal (kcal)
• What mass of aluminum can be melted by
the addition of 250. cal of heat? The heat
of fusion of aluminum is 94.5 cal/g
Q= Hf x m
m= Q/Hf
M=250.cal/ 94.5 cal/g
M= 2.65 g