physics unit 6: thermodynamics. “thermodynamics” is derived from greek meaning “movement of...
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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… Energy = Heat
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.
Specific Heat Capacity
What is it? The resistance to change in
temperature of a substance.
The Equation:
Q = mcΔT
Where:Q = heat addedm = mass of the samplec = specific heat capacityΔT = change in temperature
Examples:
1. How much heat energy is required in order to raise the temperature of a 0.5 kg iron nail from 25oC to 80oC?
Q = mcΔTQ = (0.5)(460)(55) = 12,650 Joules
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.