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 32 o F and boils at 212 o F Celsius – Water freezes at 0 o C and boils at 100 o C 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 Evaporation Boiling 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 L f (or H f ) Latent Heat of Vaporization The amount of energy required to change a unit mass from liquid to gas (and vice versa). Abbreviated L v (or H v ) LvLv LfLf
Phase Changes Latent Heat Equation: Q = mL Where: Q = heat added during phase change m = mass of sample L = Latent Heat (of fusion or vaporization) Examples: