Phase Change

1
Phase Change

• Chemical Interactions
• Grade 8

2
Melting and Freezing

• Melting a change of state from solid to liquid.
• Energy is transferred to the solid and gains
  kinetic energy.
• Freezing a change of state from liquid to solid.
• Energy is transferred from the liquid and looses
  kinetic energy.

3
Kinetic Energy

• Change of state is the result of change of
  kinetic energy of the particles of a material.
• Nothing changes during change of state except the
  motion of the particles.
• The particles do not melt, freeze, contract,
  expand, or change into any other kind of
  particles.
• Change of state is not a chemical reaction, so no
  new products are forming.

4
Water

• Water freezes at 0Celsius.
• Water melts at 0Celsius.
• Substances do not have to be cold to freeze or
  hot to melt phase change is a relationship
  between the particles in a substance.

5
Heat of Fusion

• Heat of Fusion The energy needed to melt a
  substance.
• For water, the heat of fusion is 80cal/g.
• A lot of heat must be transferred from water at
  0Celsius to change it to ice at 0Celsius.
• You must transfer 80 cal away from 1 gram of
  water at 0C go change it into a gram of ice at
  0C.

6
Condensation

• Condensation The process of changing state from
  gas to liquid.
• When energy transfers from the water vapor
  particles, their kinetic energy decreases.
• The particles stop flying around and bunch
  together as liquid.

7
Evaporation

• Evaporation changing state from liquid to gas.
• When energy transfers to the particles in liquid
  water, they gain kinetic energy.
• When a particle gains enough kinetic energy to
  escape other particles, it flies off as water
  vapor particle.

8
Phase Change - A story

1. Heat energy in the warm water increased the
   kinetic energy of some water particles.
2. The particles with sufficient kinetic energy fly
   free of the bunched particles in liquid water.
   This phase change is evaporation.

9
Phase Change - A story

• 3) Water vapor particles strike the cold ice cup.
  Energy transferred from the particles to the cold
  cup.
• 4) Energy transfer from water vapor particles
  reduces the kinetic energy of particles. They
  stop flying and bunch up with other water
  particles to form liquid water. This phase change
  is condensation.

10
Phase Change - A story

• 5) Salt added to ice makes it colder. Energy
  transfers from liquid water particles. The
  kinetic energy of particles is reduced.
• 6) Reduced kinetic energy prevents particles from
  moving over and around other particles, so they
  are locked in place. Liquid water changes into
  solid ice. This phase change is freezing.

11
Phase Change - A story

• What will happen when all of the ice inside the
  cup melts?

12
Phase Change - A story

• Water inside the cup will receive energy from the
  air particles and warm up.
• Energy will transfer from the cup to the ice on
  the outside of the cup.
• The kinetic energy of the particles in the frost
  will gain kinetic energy.
• When the particles have enough kinetic energy to
  move over and around one another, the water will
  change state to liquid. This phase change is
  called melting.

13
Melting vs. Dissolving

• Melting
• When a material changes from a state from solid
  to liquid.
• Heat and Energy Transfer are needed to change
  state.
• Physical change to substance.
• Substance does not change in chemical
  composition.

• Dissolving
• When a solid material is placed in liquid, and
  the solid material disappears into the liquid.
• Water or Liquid is needed to dissolve a
  substance.
• Physical change to substance.
• Substance does not change in chemical composition.