Kinetic Molecular Theory and the Gas Laws

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Kinetic Molecular Theory and the Gas Laws

• Phases of Matter, Kinetic Molecular Theory, and
  Temperature
• Gas Laws
• Phase Changes

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Phases of Matter

• There are four phases of matter
• 1. Solid
• 2. Liquid
• 3. Gas
• 4. Plasma
• The state of matter depends on the motion of the
  molecules that make it up.

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Solids

• Solids are objects that have definite shapes and
  volumes. The atoms or molecules are tightly
  packed, so the solid keeps its shape. The
  arrangement of particles in a solid are in a
  regular, repeating pattern called a crystal.

Microscopic picture of a solid.
4
Liquids

• The particles in a liquid are close together, but
  are able to move around more freely than in a
  solid. Liquids have no definite shape and take
  on the shape of the container that they are in.

Microscopic picture of a liquid.
5
Gases

• A gas does not have a definite shape or volume.
  The particles of a gas have much more energy than
  either solids or liquids and can move around
  freely.

Microscopic picture of a gas.
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Plasma

• Plasma is a gas-like mixture of positively and
  negatively charged particles. Plasma is the most
  commonly found element in the universe, making up
  99 of all matter. It is found in stars, such as
  the sun, and in fluorescent lighting. Plasma
  occurs when temperatures are high enough to cause
  particles to collide violently and be ripped
  apart into charged particles.

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Kinetic Molecular Theory of Matter

• All matter is made of particles that are in
  constant motion. The more energy the particles
  have, the more freely they move around. This
  freedom that molecules have is the determining
  factor for their state of matter. Therefore,
  solids have the least amount of energy. Liquids
  come next followed by gases. Finally, plasma has
  the most energy of any state of matter.

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Temperature

• Temperature is a measure of the amount of the
  average kinetic energy of the particles in
  matter. The more kinetic energy the particles
  have, the higher the temperature. The
  temperature of particles are usually recorded in
  one of three ways
• 1. Fahrenheit (ºF)
• 2. Celsius (ºC)
• 3. Kelvin (K)
• Do you remember which is the standard unit????

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Fahrenheit

• Developed by Daniel Gabriel Fahrenheit, who is
  best known for inventing the alcohol thermometer
  and mercury thermometer in the early 1700s. It
  is based on 32º for the freezing point of water
  and 212º for the boiling point of water. The
  interval between the freezing and boiling points
  are divided into 180 parts.
• The conversion from Celsius to Fahrenheit is
• ºF (9/5 ºC) 32

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Celsius

• Scale developed by Anders Celsius in the early to
  mid-1700s, working from the invention of
  Fahrenheit's thermometers. The Celsius scale is
  based on 0º for the freezing point of water and
  100º as the boiling point. The interval between
  the freezing and boiling points are divided into
  100 parts.
• The conversion from Fahrenheit to Celsius is
• ºC (5/9)(ºF-32)
• The conversion from Kelvin to Celsius is
• ºC K-273

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Kelvin

• Developed by William Thompson Kelvin in 1848,
  Kelvin is a temperature scale having an absolute
  zero below which temperatures do not exist. At
  0K, all molecules cease any type of motion (as in
  the temperature of outer space). It corresponds
  to a temperature of -273 on the Celsius
  temperature scale. The Kelvin degree is the same
  size as the Celsius degree, so the freezing point
  of water is at 273K and the boiling point is at
  373K. http//www.allmeasures.com/temperature.html

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Kinetic Theory of Gases

• The constant motion of particles in a gas allows
  a gas to fill a container of any shape or size.
• The motion of one particle is unaffected by the
  motion of other particles unless the particles
  collide
• Forces of attraction among particles in a gas can
  be ignored under ordinary conditions

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Explaining the Behavior of Liquids

• Particles in liquids also have kinetic energy but
  are more tightly packed than particles in gas.
• And unlike gases, attractions between particles
  in a liquid do affect the movement of particles
• A liquid takes the shape of its container because
  particles in a liquid can flow to new locations.
  The volume of a liquid is constant because forces
  of attraction keep the particles close together.

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Explaining the Behavior of Solids

• Solids have a definite volume and shape because
  particles in a solid vibrate around fixed
  locations.
• There is a strong attraction among the atoms
  that restrict their motion and keep each atom in
  a fixed location relative to its neighbors.

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The Behavior of Gases

• The behavior of gases can be explained by the way
  their particles interact with each other and the
  environment around them.
• The particles are constantly colliding with one
  another and other objects. Since the molecules
  have mass, there is a certain amount of pressure
  being applied.
• As the volume of the gas and/or the temperature
  of the gas change, so does its behavior.

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Gas Laws

• The result of a force distributed over an area.
• SI unit for pressure pascal (Pa) N/m2
• (one kilopascal kPa 1000 Pa)

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Factors that Affect Pressure of an Enclosed Gas

• Temperature
• Volume
• Number of Particles

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Temperature

• Raising the temperature of a gas will increase
  its pressure if the volume of the gas and the
  number of particles are constant

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Volume

• Reducing the volume of a gas increase its
  pressure if the temperature of the gas and the
  number of particles are constant.

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Number of Particles

• Increasing the number of particles will increase
  the pressure of a gas if the temperature and the
  volume are constant.

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Boyles Law

• Boyles Law shows the relationship between the
  volume and pressure of a gas
• The volume of a fixed amount of gas varies
• inversely with the pressure on the gas.
• If the pressure increases, the volume decreases
  if the pressure decreases, then the volume
  increases.
• P1V1P2V2

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Boyles Law
From Physical Science, Merrill, 1993
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A Graph of Boyles Law
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Charless Law

• Charless Law shows the relationship between the
  temperature and volume of a gas
• The volume of a fixed amount of gas varies
• directly with the temperature of the gas.
• If the temperature increases, the volume
  increases if the temperature decreases, then the
  volume decreases.
• V1 V2
• T1 T2

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A Graph of Charless Law
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26
Phase Changes

• A reversible physical change that occurs when a
  substance changes from one state of matter to
  another.
• The temperature of a substance doesnt change
  during a phase change.
• Energy is either absorbed or released during a
  phase change.
• Heat of fusion energy a substance must absorb
  in order to change from a solid to a liquid.

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Six Common Phase Changes

• Melting- temperature at which a substance changes
  from solid to liquid.
• Freezing temperature at which a substance
  changes from a liquid to a solid.
• Vaporization substance changes from a liquid to
  a gas. (Heat of Vaporization- energy a substance
  must absorb in order to change from a liquid to a
  gas.)

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• 4. Condensation- substance changes from a gas or
  vapor to a liquid.
• 5. Sublimation substance changes from a solid
  to a gas or vapor without changing to a liquid
  first (endothermic)
• 6. Deposition substance changes directly into a
  solid without first changing to a liquid
  (exothermic)

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