Heating Curve



A
  • Naphthalene is in solid state at any temperature below its melting point.
  • The particles are very closely packed together in an orderly manner.
  • The forces between the particles are very strong. The particles can only vibrate at a fixed position.
A-B
  • As the naphthalene is heated, heat energy is converted to kinetic energy.
  • Kinetic energy increases and the molecules vibrate faster about their fixed positions and the temperature increases.
B
  • Naphthalene is still in solid state.
  • Naphthalene molecules have received enough energy to overcome the forces of attraction between them.
  • Some of the particles that gain enough energy begin to move freely.
  • Naphthalene starts to melt and changes into a liquid.
B-C
  • Naphthalene exists in both solid and liquid states.
  • The temperature remains constant because the heat that supplied to naphthalene is used to overcome the forces of attraction that hold the particles together.
  • The constant temperature is called the melting point.
  • The heat energy that absorbed to overcome the intermolecular forces is named as the latent heat of fusion.
C
  • All the naphthalene has completely melted.
  • Solid naphthalene has turned into liquid.
C-D
  • Naphthalene is in liquid state.
  • As the liquid naphthalene is heated, the molecules gain more heat energy and the temperature continues to increase.
  • The particles move faster and faster because their kinetic energy is increasing.
D
  • Naphthalene still exists in liquid state.
  • Naphthalene molecules have received enough energy to overcome the forces of attraction between the particles in the liquid.
  • Some of the naphthalene molecules start to move freely and liquid naphthalene begin to change into gas.
D-E
  • Naphthalene exists in both liquid and gaseous states.
  • The temperature remains unchanged.
  • The is because the heat energy absorbed is used to overcome the intermolecular forces between the particles of the liquid rather than increase the temperature of the liquid.
  • This constant temperature is the boiling point.
E
  • All the naphthalene has turn into gas.
E-F
  • The gas particles continue to absorb more energy and move faster.
  • The temperature increases as heating continues.


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