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Pre-AP Physics Unit 6: Thermodynamics
“Thermodynamics”
Is derived from Greek meaning “movement of heat.”
The First Law of Thermodynamics
Official Definition:When heat flows in or out of a system, the energy it gains or loses is equal to the amount of heat transferred.
Or… Heat = Energy !
Is analogous to the Law of Conservation of Energy
We are now dealing with Internal Energy
Temperature:
What is it? How “Hot” or “Cold” a substance is.
Temperature represents the average translational kinetic energy of the individual particles in a system.
The Temperature Scales Fahrenheit – water freezes at 32oF and boils at 212oF
Celsius – Water freezes at 0oC and boils at 100oC
Kelvin – is based off of Absolute Zero
Absolute Zero So cold that all particles stop moving!
Total energy of the particles is 0.
Temperature:
Specific Heat Capacity
What is it?
The resistance to change in temperature of a substance.
The Equation:
Q = mcΔT
Examples:
The Second Law of Thermodynamics Official Definition:
Heat, of itself, never flows from a colder object to a warmer object.
Energy always flows from Hot to Cold
This law is also called the Law of Entropy
What is Entropy?
The amount of disorder in a system
The universe is always moving towards more entropy
Examples:
Ice melting
Liquid water evaporating
It takes Work (energy) to decrease Entropy
Types of Heat Transfer
Conduction
Heat transfer between materials that are in direct contact with each other.
Convection
Transfer in a fluid by movement of the substance itself.
Radiation
Energy transmitted by electromagnetic waves.
Phase Changes
The States of Matter:
Phase Changes
Types of Phase Changes:
Melting
Evaporation
Condensation
Boiling
Sublimation
Melting
Condensation
EvaporationBoiling
Sublimation
Phase Changes
How do you change the melting point or boiling point of a substance?
Add a solute
Change the pressure
Phase Changes
Energy During Phase Changes
What happens to the temperature of water as heat is added?
It Increases.
What happens to the temperature during a phase change? It remains constant.
Phase Changes
Latent Heat
Latent Heat of Fusion
The amount of energy required to change a unit mass of any substance from a solid to a liquid (and vice versa).
Abbreviated Lf (or Hf)
Latent Heat of Vaporization
The amount of energy required to change a unit mass from liquid to gas (and vice versa).
Abbreviated Lv (or Hv)Lv
Lf
Phase Changes
Latent Heat
Equation:Q = mL
Where:Q = heat added during phase changem = mass of sampleL = Latent Heat (of fusion or vaporization)
Examples:
