HeatChapter 9 Thermal Energy

Kinetic and Potential Energy

• Kinetic energy- energy of motion

• potential energy – Is the certain amount of energy that Molecules have that is ABLE to be changed to kinetic energy

*Thermal Energy

• Both the potential energy + the kinetic energy of all the molecules in an object is: Thermal Energy.

What is Temperature?

• Temperature- is a measure of the average movement of molecules(kinetic energy)

• (You know it as “How hot or cold something is”)

–Higher temperatures mean faster moving molecules in a substance

Temperature Scales

• Three Common Temperature Scales (units)– Fahrenheit is used mainly in the United States

– Celsius is based on water’s freezing and boiling points

– Kelvin, uses zero as absolute zero, the lowest temperature an object can have.

Converting Temperatures

• Convert Fahrenheit to CelsiusC = 5/9 ( Temperature in Fahrenheit - 32)

• Convert Celsius to Fahrenheit F = 9/5 ( Temperature in Celsius) + 32

• Convert Celsius to KelvinK= Temperature in Celsius + 273

PEMDAS DOES COUNT!!!!!

Thermal Expansion

• When most substances are heated they expand, The amount they expand depends on the material and temperature

– That means the molecules speed up and tend to move farther apart

*This means things that are cooled slow down their particles, which get closer….causing it to contract or shrink

Heat Transfer Chapter 9

What is Heat?

• Heat- A form of energy (thermal) made by the motion of molecules. – The more movement of molecules the more heat

energy– Heat energy has the ability to do work

Finishing Heat’s Definition

• Heat: is thermal energy that is TRANSFERRED from one object to another when the objects are at different temperatures.

• So there must be a difference in temperatures for heat to transfer!

DO NOT WRITEHeat & States of Matter

• Solids have vibrating particles, not moving freely,– add heat and the solids melt, to liquids

• Liquids have less restricted moving particles– Add heat and the liquid evaporates

» To the most freely moving particles of a gas

• The opposite is true when you remove heat, from gas to liquid to solid

*Thermometers

Transferring Heat• Heat ONLY flows from warmer objects to

cooler objects– Heat NEVER flows from colder objects to

warmer objects– Heat transfer occurs in three ways• Conduction• Radiation• Convection

Conduction• Conduction- This is the transfer of heat by

direct contact…– …This is done by the contact between particles of

high kinetic (moving) energy to particles of low kinetic energy

– Transfer will continue until all particles have the same kinetic energy and are the same temperature

– Occurs more easily in solids and liquidsExample:

Attempting to eat a hot pocket and you burn your mouth

Radiation • Radiation- Transfer of energy by electromagnetic waves.• This can occur in space

or through matter since it does not require particles to transfer the energy

• This is how the sun’s energy reaches Earth

Convection

• Convection- Heat transfer that occurs in moving fluids (liquids and gases), the movement of molecules from one part of a material to another.

• Hot liquids & gases rise while cold ones fall. This creates currents that carry the heat energy

• Wind is caused by convection

Good and Poor Conductors

• Poor Heat Conductors- Wood- Plastic- Glass- Gases

• Good Heat Conductors-Most metals

Conductors: material that easily transfers heat

Insulation• Insulation: is used to reduce the amount of

heat loss by conduction• Poor Conductors are good insulators• Materials that trap air are good insulators

DO NOT WRITEHeat Transfer

• Used in heating systems of homes and other buildings

• Used in Cooling Systems too• Heating• Fireplace-Radiation• Steam Heating-Uses all 3• Hot Water Heating-Uses all 3• Electrical• Solar

• Cooling• *Uses evaporation to absorb heat• Air Conditioners• Refrigerators

Heating an Object

• Specific Heat: This is the amount of heat needed to raise the temperature of 1 kg of a substance by 1 Degree Celsius (depends on the material)

• Thermal Equilibrium: This is when there is no heat movement between two things, because both objects have reached an equal amount of thermal energy.

Three Laws of Thermodynamics

• First Law of Thermodynamics: Aka> The Law of Conservation of Energy. The amount of energy in the universe remains constant.

• Second Law of Thermodynamics: Any process will tend to increase the amount of entropy (chaos) in the universe!!!!

• Third Law of Thermodynamics: As the temperature approaches absolute zero, the entropy of a system approaches its minimum.