The States of Matter The Gas Laws Kinetic Theory of Matter

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The States of Matter The Gas Laws Kinetic
Theory of Matter
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States of Matter
Solid Liquid Gas Plasma
Matter can exist in these 4 states. Changes of
state may occur under specific conditions.
Liquid into Gas evaporation and boiling Solid
into Liquid melting Solid into Gas
sublimation Plasma has its own characteristics
and quite different from the other three states
and will not be covered here in detail.
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Phase changes by Name
Critical Point
Pressure (kPa)
Temperature (oC)
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Triple point

• The triple point of a substance is the
  temperature and pressure at which three phases
  (gas, liquid, and solid) of that substance may
  coexist in thermodynamic equilibrium. The single
  combination of pressure and temperature at which
  pure water, pure ice, and pure water vapour can
  coexist in a stable equilibrium occurs at exactly
  273.16 kelvins (0.01 C) and a pressure of
  611.73 pascals (ca. 6.1173 millibars,
  0.0060373057 atm). At that point, it is possible
  to change all of the substance to ice, water, or
  vapour by making infinitesimally small changes in
  pressure and temperature.
• Triple point is where all 3 curves meet, the
  conditions where all 3 phases exist in
  equilibrium!
• A critical point, also called a critical state,
  specifies the conditions (temperature, pressure)
  at which the liquid state of the matter ceases to
  exist.

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The Nature of Gases

• What happens when a substance is heated?
  Particles absorb energy!
• Some of the energy is stored within the
  particles- this is potential energy, and does not
  raise the temperature
• Remaining energy speeds up the particles
  (increases average kinetic energy)- thus
  increases temperature

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• For gases, it is important to relate measured
  values to standards
• Standard conditions are defined as a temperature
  of 0 oC and a pressure of 101.3 kPa, or 1 atm
• This is called Standard Temperature and Pressure,
  or STP

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Kinetic Theory of Gases
All matter is composed of tiny particles that are
in constant motion.

• Gas molecules
• are small compared with the average distances
  between them
• collide without loss of kinetic energy
• exert almost no forces on one another outside of
  collisions

Thus, a gas is mostly an empty space
The absolute temperature of a gas is proportional
to the average kinetic energy of its molecules
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Why Molecules Keep Moving?
Motion is affected by friction
When friction is applied, it converts kinetic
energy into heat
Heat is molecular energy!
Thus, there is no change in molecular energy by
friction ? molecular motion is unstoppable
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Brownian Motion

• Random movement of solid particles suspended in a
  liquid or in a gas called Brownian Motion.
• A suspended particle is constantly and randomly
  bombarded from all sides by molecules of the
  liquid or the gas.

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Maxwell- Boltzmann Distribution

• Kinetic energy of molecules is only dependent on
  the speed of the particles.
• Remember Kinetic Energy ½mv2
• In any particular mixture of moving molecules,
  the speed will vary a great deal, from very slow
  particles (low energy) to very fast particles
  (high energy). Most of the particles however will
  be moving at a speed very close to the average.
• The Maxwell-Boltzmann distribution shows how the
  speeds (and hence the energies) of a mixture of
  moving particles varies at a particular
  temperature.

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Points to notice No molecules at zero energy,
Few molecules at high energy, No maximum energy
value

• For the reaction to occur, the particles involved
  need a minimum amount of energy - the Activation
  energy . If a particle is not in the shaded
  area, then it will not have the required energy
  so it will not be able to participate in the
  reaction.

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• The particles in any collection have a wide range
  of kinetic energies, from very low to very high-
  but most are somewhere in the middle, thus the
  term average kinetic energy is used
• The higher the temperature, the wider the range
  of kinetic energies
• Kinetic Energy and speed of molecules are
  directly proportional.
• As K.E. Speed of molecules
• Is there a point where they slow down enough to
  stop moving?
• The particles would have no kinetic energy at
  that point, because they would have no motion
• Absolute zero (0 K, or 273 oC) is the
  temperature at which the motion of particles
  theoretically ceases
• This has never been reached, but about 0.5 x 10-9
  K has been achieved

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• The Kelvin temperature scale reflects a direct
  relationship between temperature and average
  kinetic energy
• Particles of He gas at 200 K have _____________
  average kinetic energy as particles of He gas at
  100 K.

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Boyles Law
Gas is the simplest state of matter to study

• Boyles law relates gaseous volume and pressure
  under constant temperature

p1 ? initial pressure, p2 ? final pressure V1 ?
initial volume, V2 ? final volume
p1 V2 --- ---- p2 V1
p1V1 p2V2 at constant temperature(T)
number of moles(n)
or
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Charles Law
Changes in volume are related to the temperature
of gas under a constant pressure
P1 P2 --- ---- T1 T2
At constant V and n V volume n of particles
P1 initial pressure, p2 final pressure T1
initial temperature T2 final temperature
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Gay Lussacs Law
Gay Lussacs law relates gaseous teperature and
pressure under constant temperature
V1 V2 --- ---- T1 T2
At constant P and n P pressure n i-of
particles
V1 initial volume, V2 final volume T1 initial
temperature T2 final temperature
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Absolute Zero Temperature
It is impossible to achieve such a low
temperature (?273oC)
Gases turn into liquids before this temperature
is reached
The temperature ?273oC is called absolute zero
Absolute temperature is temperature measured
above absolute zero in degrees celsius (the
Kelvin scale)
V1 V2 --- ---- T1 T2
at constant pressure ? Charles law
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Ideal Gases

• A gas that obeys PVnRT is called Ideal Gas.
• The volume and the attractive forces between the
  particles of an Ideal Gas can be neglected.
• Real gases can only obey PVnRT at low Pressure
  and high Temperature.

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Ideal Gas
Combined Boyles and Charles laws give the ideal
gas law
p1 V1 p2 V2 ------- ------- T1
T2
At constant T (T1 T2) we have Boyles law At
constant p (p1 p2) we have Charles law
p V ----- const T
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Daltons Law of Partial Pressures

• The total pressure of a mixture of gases is equal
  to the sum of the pressures that each gas would
  exert if it occupied the space alone.
• P total P 1 P 2 P 3.P n
• P1 n1 P1 V1
• P total n total P
  total V total

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Diffusion

• Movement from a region of high concentration to
  one of low concentration . The rate of diffusion
  of a gas decreases as its molar mass increases.

Effusion

• The escape of a gas from a container into a lower
  pressure through a small hole. Effusion rate is
  the same as diffusion rate and it decreases with
  increasing molar mass.

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• Solids and liquids differ in their response to
  temperature
• However, at any given temperature the particles
  of all substances, regardless of their physical
  state, have the same average kinetic energy
• What happens to the temperature of a substance
  when the average kinetic energy of its particles
  decreases?

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The Nature of Liquids

• The conversion of a liquid to a gas or vapor is
  called vaporization
• When this occurs at the surface of a liquid that
  is not boiling, the process is called evaporation
• Some of the particles break away and enter the
  gas or vapor state but only those with the
  minimum kinetic energy

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• A liquid will also evaporate faster when heated
• Because the added heat increases the average
  kinetic energy needed to overcome the attractive
  forces
• But, evaporation is a cooling process
• It is an endothermic process
• Cooling occurs because those with the highest
  energy escape first

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The Nature of Solids

• Amorphous solids lack an ordered internal
  structure
• Rubber, plastic, and asphalt are all amorphous
  solids- their atoms are randomly arranged
• Another example is glass- substances cooled to a
  rigid state without crystallizing

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• In a crystal, the particles (atoms, ions, or
  molecules) are arranged in a orderly, repeating,
  three-dimensional pattern called a crystal
  lattice
• All crystals have a regular shape, which reflects
  their arrangement

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• Glasses are sometimes called supercooled liquids
• The irregular internal structures of glasses are
  intermediate between those of a crystalline solid
  and a free-flowing liquid
• Do not melt at a definite mp, but gradually
  soften when heated

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Entropy
Entropy measures how much energy is dispersed
in a particular process (at a specific
temperature). 
A liquid has more disorder than a solid. A gas
has more disorder than a liquid.
The entropy of an isolated system cannot decrease.
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A hot frying pan cools down when it is taken off
the kitchen stove.

• All types of energy behave like the energy in
  that hot pan unless somehow they are hindered
  from spreading out. They tend not to stay
  concentrated they flow toward becoming dispersed
  -- like electricity in a battery or a power line
  or lightning, wind from a high pressure weather
  system or air compressed in a tire. All these
  different kinds of energy spread out if they can.
  The reason for their occurring is the same, the
  tendency for concentrated energy not to stay
  localized, to disperse if it has a chance and
  isn't hindered somehow.   

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• Edited by Aysun Simpson