Energy & Phase Changes

Energy

Law of Conservation of Energy
Heat : Involves transfer of energy
           Flows from high temperature to low temperature
           Describe changes to the motion of particles when heat added or taken away
Temperature:  measure of average kinetic energy
Kelvin = Celsius + 273
Absolute zero = 0 Kelvin

Endothermic Reaction: Needs heat to occur

Exothermic Reaction: Produces heat

Intermolecular Forces - Bonds between molecules
    Forces must be overcome to change phase

Dipole-Dipole

• Between polar covalent molecules

Hydrogen bonding

• Between polar molecules where hydrogen is bonded to a very E.N. atom (F, O, N)
• Strongest intermolecular force
• Creates higher melting and boiling point

Van der Waals forces

• Attraction between non-polar molecules
• Weakest attractive force
• Only felt when molecules are close together
• Substances have lowest MP/BP
• Strongest when there are more electrons in the molecule

Matter
Three Phases of Matter and Their Properties: Solids, Liquids Gases
Phase Changes: Melting (fusion), Vaporization, Condensation, Freezing, Sublimation, and Deposition

Heating & Cooling Curves (Change of Phase Diagrams)

Kinetic Energy does not change during phase changes
KE increases when temperature increases
PE changes during a phase change

The Heat Equations
Measuring Heat Energy when Temperature Changes
Q=mc /\ T
Measuring Heat Energy During Phase Changes
Q=mHv        Q=mHf

Energy and Phase Change Regents Questions