Lecture16: Phase

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Lecture-16 Phase Temperature Changes
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Phase Temperature Changes

• Heat is a form of energy.

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Phase Temperature Changes

• Heat is the form of energy that flows between two
  samples of matter that are at different
  temperatures.

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Phase Temperature Changes

• Heat always flows from the sample of matter at
  higher temperature to the sample of matter at
  lower temperature until both samples reach the
  same temperature.
• Heat is measured in units called calories (cal)
  or joules (J).

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Phase Temperature Changes

• Temperature is NOT a form of energy.
• Temperature is a measure of the average KE of the
  particles of the sample of matter.
• If the particles that make up a sample of matter
  are moving slowly (have a low average KE), then
  the sample has a low temperature.
• If the particles that make up a sample of matter
  are moving quickly (have a high average KE), then
  the sample has a high temperature.
• Temperature is measured in units called degrees
  fahrenheit (oF), degrees celsius (oC), or kelvin
  (K).

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Phase Temperature Changes

• Heat and temperature are two different things.
• A cold lake contains much more heat in it than a
  pan of hot water does.

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Phase Temperature Changes

• There is a temperature to heat relationship
• If a samples temperature has increased, then the
  sample HAS absorbed heat.
• If a samples temperature has decreased, then the
  sample HAS released heat.
• The heat to temperature relationship is NOT as
  clear
• If a sample absorbs heat, then the samples
  temperature may or may NOT increase.
• If a sample releases heat, then the samples
  temperature may or may NOT decrease.

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Phase Temperature Changes

• How can a sample of matter absorb heat and not
  experience an increase in temperature?
• How can a sample of matter release heat and not
  experience a decrease in temperature?

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Phase Temperature Changes

• During a phase change a sample of matter IS
  absorbing or releasing heat, but it does NOT
  experience a change in its temperature!

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Phase Temperature Changes

• While ice is melting heat is being absorbed, but
  temperature is always at 0.0oC!

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Phase Temperature Changes

• While ice is boiling heat is being absorbed, but
  temperature is always at 100.0oC!

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Phase Temperature Changes
Heating the gas (Only gas phase present)
Boiling point temp.
T E M P E R A T U R E
Heating the liquid to gas
BOILING
Heating the liquid up to its boiling point (Only
liquid phase present)
Melting point temp.
Heating the solid to liquid
MELTING
Heating the solid up to its melting point (Only
solid phase present)
T I M E
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Phase Temperature Changes
Heating the gas (ONLY GAS)
Boiling point temp.
T E M P E R A T U R E
Heating the liquid to gas
BOILING
Melting point temp.
Heating the liquid up to its boiling point (ONLY
LIQUID)
Heating the solid to liquid
MELTING
Heating the solid up to its melting point (ONLY
SOLID)
T I M E
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Phase Temperature Changes

• When a sample of matter absorbs heat while in a
  single phase, the absorbed heat allows the
  particles of the sample of matter to move faster.
• When a sample of matter absorbs heat while
  undergoing a phase change, the absorbed heat
  allows the particles of the sample of matter to
  move and to position themselves differently.

Thus, the temperature increases!
Thus, the phase changes!
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Phase Temperature Changes

• It takes heat to increase the temperature of a
  sample of matter.
• It also takes heat to change the phase of a
  sample of matter.
• Remember...
• ... When heating a sample of matter during a
  temperature change, the phase can NOT be
  changing!
• AND
• ... When heating a sample of matter during a
  phase change, the temperature can NOT be changing!