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 = mcΔT

Q = (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.