Chapter 16 Thermal Energy & Heat

16.1 Thermal Energy and Matter Objectives: 1. Explain how heat and work transfer energy 2. Relate thermal energy to the motion of particles that make up a material 3. Relate temperature to thermal energy and to thermal expansion 4. Calculate thermal energy, temperature change, or mass using the specific heat equation

How Heat and Work Transfer Energy Def: heat is the transfer of thermal energy from one object to another because of temperature difference Heat flows spontaneously from hot objects to cold objects

How Heat and Work Transfer Energy Def: temperature is a measure of how hot or cold an object is compared to a reference point On the Celsius scale, the reference points are the freezing point and boiling point of water

Motion of Particles and Thermal Energy Another reference point is called absolute zero Absolute zero is on the Kelvin scale Temperature is related to the average kinetic energy of particles in an object due to their random motions through space Celsius + 273 = K

Temperature, Thermal Energy & Expansion Def: thermal expansion is 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

Frozen waves and bubbles https://www.youtube.com/watch?v=OSXJyqM8dV8 https://www.youtube.com/watch?v=kcUYvUpc58E

Specific Heat Def: Specific heat is the amount of energy transferred as heat that will raise the temperature of 1 g of substance by 1 K Little c is the symbol for specific heat, & specific heat is a physical property The units for specific heat are J/g-K We will assume that volume & pressure do not change in order to do calculations involving the formula energy = specific heat x mass x temperature change OR energy = cm∆t (the ∆ means change & is the final temperature minus the initial temperature)

Calorimetry Lab

16.2 Heat and Thermodynamics Objectives: 1. Describe conduction, convection and radiation & identify which one of these is occurring in a given situation 2. Classify materials as thermal conductors or thermal insulators 3. State the 3 laws of thermodynamics 4. Apply the first & second laws to given situations

Conduction, Convection & Radiation Def: conduction is the transfer of thermal energy with direct contact Conduction is the heat energy transfer between particles as they collide within a substance or between objects in contact (ex: touching a hot mug of coffee with your hands

Def: a thermal conductor is a material that conducts thermal energy well Def: a thermal insulator is a material that conducts thermal energy poorly Ex: Iron in a pot is a thermal conductor; the oven mitt you use to pick it up is a thermal insulator

Def: convection is the transfer of thermal energy when particles of a fluid move from one place to another Convection is the heat energy transfer by movement of fluids with different temperatures (ex: warm air rising, cools, condenses, becomes dense and sinks)

A convection current is the flow of liquid due to heated expansion followed by cooling and contraction Convection currents are important in many natural cycles such as ocean currents, weather systems, and movements of hot rock in Earth’s interior in the asthenosphere under the lithospheric plates

Convection currents

Def: radiation is the transfer of energy by waves moving through space Radiation does not require physical contact between objects

Radiation does not involve movement of matter & can take place in a vacuum (ex: the radiation we receive from the sun is in a vacuum) All objects radiate energy As an object’s temperature increases, the rate at which it radiates energy increases

Objects radiate heat / infrared

Three Laws of Thermodynamics Def: thermodynamics is the study of conversions between thermal energy and other forms of energy The first law, also known as Law of Conservation of Energy, states that energy cannot be created or destroyed in an isolated system. 

2nd Law of thermodynamics The second law of thermodynamics states that the entropy of any isolated system always increases. Entropy (S), on the other hand, is a measure of the "disorder" of a system.

An increase in entropy (disorder) Entropy and the Origin of the Universe – NOVA https://www.youtube.com/watch?v=LzvkO5ai9YQ

The Third Law of Thermodynamics states that the entropy of a perfect crystal at absolute zero is exactly equal to zero. Scientists have gotten close, but have not been able to do this

16.3 Using Heat Objectives: 1. Describe heat engines and explain how they convert thermal energy to mechanical energy 2. Describe how different heating systems operate 3. Describe how cooling systems operate

Heat Engines Def: a heat engine is any device that converts heat into work The two main types of heat engines are the external combustion engine and the internal combustion engine

Steam Engine is external Def: the external combustion engine is an engine that burns fuel outside the engine

Def: an internal combustion is a heat engine in which fuel burns inside the engine Ex: your car https://www.youtube.com/watch?v=Rg87DSRzfiU

Both types of engines have pistons that move either back and forth or up and down Some waste energy is discharged

Heating & Cooling Systems The principles of transfer of heat allow us to design buildings that can be heated and cooled efficiently Recall that total energy is conserved whether it is transferred due to work, heat or both This is called the first law of thermodynamics Secondly, energy transferred as heat always moves from an object of high temperature to an object at low temperature

A heating system is any device or process that transfers energy to a substance to raise the temperature of the substance Def: a central heating system heats many rooms from one central location (often the basement) Most heating systems use convection to distribute thermal energy

Hot water heating is usually by boiler, heating oil or natural gas A pump circulates the water to radiators in each room that transfer energy by conduction Most heating systems use these principles

A refrigerator is a heat pump It transfer thermal energy from the cold food compartment to the warm room A cooling system is a device that transfers heat energy out of an object to lower its temperature How does a refridgerator work https://www.youtube.com/watch?v=EIP3pSio7-M

Air conditioners use a liquid refrigerant to decrease temperature and then transfer the warm air out Def: A refrigerant is a substance used in cooling systems that transfers large amounts of energy as it changes state How AC Works | Intelligent Design AC https://www.youtube.com/watch?v=QWD3O1TyJRg