1. Heat and States of Matter
Chapter 9:
Heat and States of Matter
Section 4: Using Thermal Energy

2. How is thermal energy used?
Using Thermal Energy 4
How is thermal energy used?
HEATING SYSTEMS
FORCED-AIR SYSTEMS
Fuel is burned in a furnace and heats a volume of air.
A fan blows the heated air through a series of large pipes called ducts.
The ducts lead to openings called vents in each room.

3. Using Thermal Energy 4
RADIATOR SYSTEMS
A radiator is a closed metal container that contains hot water or steam.
The thermal energy contained in the hot water or steam is transferred to the air surrounding the radiator by conduction.

4. ELECTRIC HEATING SYSTEMS
Using Thermal Energy 4
ELECTRIC HEATING SYSTEMS
In an electric heating system, electrically heated coils placed in floors and in walls heat the surrounding air by conduction and convection.

5. Heating and Work Increase Thermal Energy
Using Thermal Energy 4
THERMODYNAMICS
Heating and Work Increase Thermal Energy
A SYSTEM is anything you can draw a boundary around.
The energy transferred to a system is the amount of energy flowing into the system across the boundary.
The work done on a system is the work done by something outside the system’s boundary.

6. THE FIRST LAW OF THERMODYNAMICS
Using Thermal Energy 4
THE FIRST LAW OF THERMODYNAMICS
According to the FIRST LAW OF THERMODYNAMICS, the increase in thermal energy of a system equals the work done on the system plus the thermal energy transferred to the system.
The increase in energy of a system equals the energy added to the system.

7. CLOSED AND OPEN SYSTEMS
Using Thermal Energy 4
CLOSED AND OPEN SYSTEMS
A system is an OPEN SYSTEM if thermal energy flows across the boundary or if work is done across the boundary.
If NO thermal energy flows across the boundary and no outside work is done, the system is a CLOSED SYSTEM.

8. THE SECOND LAW OF THERMODYNAMICS
Using Thermal Energy 4
THE SECOND LAW OF THERMODYNAMICS
SECOND LAW OF THERMODYNAMICS states it is impossible for thermal energy to flow from a cool object to a warmer object unless work is done.

9. CONVERTING THERMAL ENERGY TO WORK
Using Thermal Energy 4
CONVERTING THERMAL ENERGY TO WORK
No device or process can convert thermal energy completely into work.

10. Using Thermal Energy 4
HEAT ENGINES
A device that converts thermal energy into work is called a HEAT ENGINE.
When thermal energy is converted into work, some thermal energy always is transferred to the surroundings.

11. INTERNAL COMBUSTION ENGINES
Using Thermal Energy 4
INTERNAL COMBUSTION ENGINES
The heat engine in a car is an internal combustion engine.
Each cylinder contains a piston that moves up and down.
Each up or down movement of the piston is called a stroke.

12. Internal Combustion Engines
Using Thermal Energy 4
Internal Combustion Engines

13. Using Thermal Energy 4
MOVING THERMAL ENERGY
Liquid coolant is pumped through an expansion valve and changes into a gas.
The cold gas is pumped through pipes inside the refrigerator.
The coolant absorbs thermal energy and the inside of the refrigerator cools.

14. Using Thermal Energy 4
ENTROPY
According to the laws of thermodynamics, work can be converted completely into thermal energy, but thermal energy cannot be converted completely into work.
ENTROPY is a measure of how spread out, or dispersed, energy is.
Entropy increases when energy becomes more spread out and less concentrated.

15. ENTROPY ALWAYS INCREASES
Using Thermal Energy 4
ENTROPY ALWAYS INCREASES
According to the entropy principle, all events that occur cause the entropy of the universe to increase.
The energy that becomes spread out is no longer useable.