HEAT & THERMAL ENERGY

1. HEAT & THERMAL ENERGY CH. 16

2. State indicator • 17. Demonstrate that thermal energy can be transferred by conduction, convection or radiation (e.g., through materials by the collision of particles, moving air masses or across empty space by forms of electromagnetic radiation).

3. Heat flows spontaneously from hot objects to cold objects Heat is also the transfer of thermal energy.

4. What is Temperature?

5. Temperature is related to the average kinetic energy of an objects particles due to their random motion through space.

6. Temperature • The  reference point on the  Kelvin scale for temperature  is absolute zero. • 0 = -273o C • Absolute zero – a temperature of 0°K. • Room temp. would be 293o K • The purpose for this is when we study gases, which have very low freezing points.

7. Thermal energy depends on mass, temperature and phase of an object.

8. Thermal expansion occurs because particles of matter tend to move farther apart as temperature increases.

9. Gas expands more than liquids and solids

11. Specific Heat The lower a material’s specific heat is, the more its temperature will rise when energy is applied. Heat needed to raise the temp. of a 1g of an object 1° Celcius.

12. Specific Heat • Unique to every material • The  lower an object’s  specific heat, the more  the temp. increases  when heat is absorbed. • Water has a large specific heat. • Needs a lot of heat to change its temp

13. Heat • Heat  is measured in Joules or calories. • One calorie is the energy the required to raise the temp. of 1g of water by 1oC. • One calorie is equal to 1.184 J • The unit for specific heat is J/g oC

14. Q  = m   c    ΔT  • Q= heat • M= mass • C= specific heat (unique for the substance) • ΔT = change in temperature

15. A calorimeter uses the principal that heat flows from hotter to colder objects until they both reach the same temperature.

16. Heat and Thermodynamics Conduction in gases is slower than liquids & solids because the particles collide less often Transfer of heat through direct contact is CONDUCTION

17. Thermal  Conductors • Material  that conducts thermal  energy well. Examples: copper & aluminum pots & pans; wood vs. tile flooring

18. Thermal  Insulators • Material  that conducts thermal  energy poorly. • Examples: air in a double pane window, wood,    fiberglass, fat

19. Convection Transfer  of heat through moving  particles in fluids  (liquids & gases). Convection currents are important in many natural cycles. Convection Current occurs when a fluid circulates in a loop as it heats and cools. Example: oven

21. Radiation Examples:  Heat from the sun,  heat lamps used in  restaurants   light colored object   Reflect heat    dark colored object   Absorb heat

22. The first law of thermodynamics ENERGY is CONSERVED!

23. The 2nd Law of thermodynamics Heat can only flow from colder to hotter if work is done on the system.

24. The 3rd Law of Thermodynamics Absolute Zero cannot be reached People are trying! Current record is down to about 90 picokelvin! That’s 9.0 x 10^(-11)

25. Temperature and Conductivity • http://www.youtube.com/watch?v=yXT012us9ng

26. 2 types of engines Internal combustion External combustion A  heat engine is any device that converts heat into work. Thermal  energy that is not  converted into work  is called waste heat. Waste  heat is lost to  the environment.

27. Internal combustion engine

28. External combustion engine

29. Most heating systems are convection to distribute thermal energy

30. Heat pumps must do work on a refrigerant in order to reverse the flow of thermal energy

31. Alternate home heating is part of our energy future!