1. Heat: Phase Changes

2. Solids Have an orderly arrangement and fixed location of particles
Particles “vibrate” in place, so they do not flow
When heat (energy) is added, particles “vibrate” faster and begin to spread apart (melt)
Most are crystalline (rigid), some are amorphous (lack an internal structure)
Examples of amorphous solids: rubber, glass

3. Liquids
Intermolecular attractions reduce movement of particles (more dense than gas)
Vaporization: turning liquid to gas
Evaporation: surface particles only
Is a cooling process (sweat)
Boiling: particles throughout liquid
Vapor pressure = atmospheric pressure (BP)
Higher altitudes=lower bp

4. Gases
Kinetic Theory:
Particles are small, hard spheres with an insignificant volume
Most of particles is rapid, constant, and random
All collisions are perfectly elastic (energy is transferred without loss)
Gas Pressure: caused by collisions with an object
SI unit: pascal (Pa)
Standard Pressure: 1 atm = 760 mmHg = kPa

5. Processes that decrease energy (exothermic):
Freezing: changing liquid to solid
Ex: Freezing Rain
Condensation: changing gas to liquid
Ex: Rain/water on the outside of a glass on a warm day
Deposition: changing gas directly to solid
Ex: Frost on the ground/Snow

6. Processes that Increase Energy (Endothermic)
Melting: turning solid to liquid
Ex: Snow melting on roads
Vaporization: turning liquid to gas
Ex: Steam rising from hot water/puddles evaporating
Sublimation: turning solid directly to gas
Ex: dry ice/loss of glaciers

7. Heat Flow
Heat = energy transferred from one object to another due to a difference in temperature
Will always flow from high to low (warmer objects to cooler objects)
The transfer of heat follows the law of conservation of energy (energy is neither created nor destroyed)
Flows between a “system” and “surroundings”

8. Endothermic Processes/Reactions
System absorbs heat from the surroundings
Chemical reactions will feel cool to the touch because it is absorbing the heat energy out of your hand
q will be positive (heat was added to the system)

9. Exothermic Processes/Reactions
System loses heat to the surroundings
Chemical reactions will feel warm to the touch because they are releasing heat to your hands
q will be negative (heat was taken from the system)