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UNIT III Lesson 3

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UNIT III Lesson 3 Phase Changes III.5 PHASE CHANGES A chemical change is a change in which NEW SUBSTANCES are formed. A physical change is a change in the ... – PowerPoint PPT presentation

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Title: UNIT III Lesson 3


1
UNIT III Lesson 3
  • Phase Changes

2
III.5 PHASE CHANGES
  • A chemical change is a change in which NEW
    SUBSTANCES are formed.
  • A physical change is a change in the
    _______________ of a substance.
  • no new substances are formed!
  • Note chemical changes are often accompanied
    by phase changes (ie physical changes may occur
    at the same time as a chemical change).

3
III.5 PHASE CHANGES
4
Let us check our understanding
  • Physical and chemical changes check!
  • http//vital.cs.ohiou.edu/steamwebsite/downloads/C
    hangeLab.swf

5
III.5 PHASE CHANGES
6
Phase changes graph
7
III.6 THE ROLE OF KINETIC ENERGY IN PHYSICAL
CHANGES
  • All molecules are constantly __________________!
  • The energy that molecules possess as a result of
    their motion is _______________________________
  • There are THREE types of Kinetic energy that a
    molecule can possess

8
  • 1. ROTATIONAL ENERGY
  • causes a molecule to rotate around one of its
    axes (no change in bond lengths or bond angles)

9
  • 2. VIBRATIONAL ENERGY
  • changes the bond lengths and/ or bond angles
    between atoms in a molecule.

10
  • 3. TRANSLATIONAL ENERGY
  • causes the molecule to travel in a straight line
    from place to place (no change in bond length or
    angles).

11
III.6 THE ROLE OF KINETIC ENERGY IN PHYSICAL
CHANGES
  • As a sample is heated, the particles gain KINETIC
    ENERGY.
  • In a solid state....
  • The increase _____________ and _____________
    causes the molecules to oscillate back and forth
    and bump into their neighbours.
  • Once the _________________ energy increases to a
    certain point (melting point), the molecules can
    overcome the bonds holding them together (bonds
    break and solid melts).

12
III.6 THE ROLE OF KINETIC ENERGY IN PHYSICAL
CHANGES
  • In the liquid state...
  • All three types of kinetic energy increase but
    the GREATEST increase is in ____________________
    energy.
  • Again, translational energy increases to a
    certain point (boiling point) and the molecules
    escape their neighbours and fly off into the gas
    phase!

13
Practice time
  • QUESTIONS p. 64 64 71
  • QUESTIONS p. 61 59 ONLY.
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