Heating and Cooling Curves and Phase Change

Phase Change

6 Types of Phase Change

• Melting = Fusion (solid to liquid)
• Freezing = Solidification (liquid to a solid)
• Boiling = Vaporization (liquid to gas)
• Gas to Liquid = Condensation
• Solid to Gas = Sublimation
• Gas to Solid = Deposition

Specific Heat of Water

• Solid (ice): 2.1 J/g°C
• Liquid (water): 4.184 J/g°C
• Gas (steam): 2.0 J/g°C

The heat (joules) added/removed during a phase change will break intermolecular forces if warming or allow intermolecular forces to form if cooling

• The freezing AND melting point of water is 0°C
• The boiling point of water is: 100°C

Heat of Fusion

• Heat (joules) absorbed when 1 gram of solid turns into a liquid (melting)
  • For H₂O, this is 334 J/g (6.02 kJ/mol)
  • If you have 1 g of ice at 0°C it will absorb 334 joules of energy before it will melt into liquid water at 0°C
  • The temperature remains constant

Heat of Vaporization/Condensation

• Heat (joules) absorbed when 1 gram of liquid turns into a gas (vaporization)
  • For H₂O, this is 2260 J/g (40.6 kJ/mol)
  • If you have 1 g of water at 0°C it will give up 2260 joules of energy before it will solidify into ice at 0°C
  • The temperature remains constant

When we do problems that involve a phase change, we use Enthalpy

• q = mΔHfus (Melting or Freezing) 
• q = mΔHvap (Vaporization or Condensation)

Calorimetry Conversions

1.0 calorie = 4.184 J                        1 kilocalorie = 1000 calories                        1kJ = 1000 Joules