16.1 Thermal Energy

Heat The transfer of thermal energy because of a temperature difference.

Flows spontaneously from hot to cold objects Heat Flows spontaneously from hot to cold objects

Temperature Review A measure of how hot or cold an object is Measured in Celsius, Kelvin, or Fahrenheit 0 Kelvin or absolute zero is the coldest possible temperature (all atoms stop moving)

Temperature Temperature is related to the average kinetic energy of the particles in an object due to their random movements

Thermal Energy The total potential and kinetic energy of all the particles (atoms) in an object

Depends on mass, temperature, and phase (solid, liquid, or gas) Thermal Energy Depends on mass, temperature, and phase (solid, liquid, or gas)

An increase in the volume of a material due to a temperature increase. Thermal Expansion An increase in the volume of a material due to a temperature increase.

Thermal Expansion Occurs when particles of matter move farther apart as temperature increases

Thermal Expansion Gases expand more than liquids. Liquids expand more than solids. Weaker particle attractions in gases make them expand more easily.

This is what makes glass thermometers work. Thermal Expansion This is what makes glass thermometers work. Alcohol expands in the tube giving you the temperature reading.

Specific Heat The amount of heat needed to raise the temperature of one gram of a material by one degree Celsius.

Specific Heat The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass.

Specific Heat Translation: When a material has a low specific heat, it takes less energy to raise its temperature.

Measured in joules per gram per degree Celsius or J/gx0C Specific Heat Measured in joules per gram per degree Celsius or J/gx0C

Q = heat absorbed by a material m = mass C = specific heat Q = m x c x ΔT Q = heat absorbed by a material m = mass C = specific heat ΔT = change in temperature

Heat and Thermodynamics Chapter 16 Heat and Thermodynamics

The transfer of thermal energy with no overall transfer of matter. Conduction The transfer of thermal energy with no overall transfer of matter. Occurs within a material or between materials that are in contact.

Slower in gases than in liquids Slower in liquids than in solids Conduction Slower in gases than in liquids Slower in liquids than in solids Because the particles collide less often

A material that conducts thermal energy well Thermal Conductors A material that conducts thermal energy well Examples: copper cooking pot, metal baking pan, tile floor

A material that conducts thermal energy poorly Thermal Insulators A material that conducts thermal energy poorly Examples: wooden spoon, air, wool, foam

Convection The transfer of thermal energy when particles of a fluid move from one place to another

Convection Currents Occurs when a fluid circulates in a loop as it heats up and then cools down. Important in many natural cycles: ocean currents, weather systems, movements of hot rock in the Earth’s mantle

The transfer of energy by waves moving through space Radiation The transfer of energy by waves moving through space Examples: the sun heating Earth, heating coil on a stove or heater

All objects radiate energy. Radiation All objects radiate energy. As an object’s temperature increases, the rate at which it radiates energy increases. Closer objects absorb more radiation and are heated more. Further away objects absorb less radiation and are heated less.

Radiation Which receives more radiation and thus has more thermal energy, Earth or Mars? Mercury or Earth? Jupiter or Saturn?

Thermodynamics The study of conversions between thermal energy and other forms of energy.

First Law of Thermodynamics Energy is conserved. When energy is added to a system it can either increase the thermal/heat energy or do work but is must be accounted for. Remember energy can be neither created nor destroyed (only transferred).

Second Law of Thermodynamics Thermal energy can flow from colder objects to hotter objects only if work is done on the system. A heat engine converts heat into work. Thermal energy that is not converted into work is waste heat.

Second Law of Thermodynamics Spontaneous changes will always make a system less orderly, unless work is done on the system. Disorder in the universe as a whole is always increasing. You can only increase order on a local level.

Third Law of Thermodynamics Absolute zero cannot be reached. The closest that has been reached was 3 billionths of a Kelvin above absolute zero. 0.000000003 K