1. Energy for Heat Transfer

2. 1 st Law of Thermodynamics Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred. You don’t get energy from nothing. The amount of energy in the beginning is equal to the amount of energy at the end, but it may be in a different form.

3. 2 nd Law of Thermodynamics Heat never spontaneously flows from a cold substance to a hot substance. In the summer heat from flows from the warm outdoors into your cool house. Your ac does not cool the outside. The outside makes your house warmer. In the winter heat flows from your warm house to the cold air outside The cold air does not make your house colder Your house makes the outdoors warmer

4. 3 rd Law of Thermodynamics No system can reach absolute zero natures lowest possible temperature where all molecular motion ceases Physicists have been within less than a millionth of 1 Kelvin, but never 0K!

5. Refrigerators Facts Cooking does not destroy poisons in food. To preserve food it must be kept cold (between 32 o F and 40 o F) and dry. Drawbacks Cost associated with purchase and operation Energy supply needed to operate Work is done in order to move thermal energy from low to high. If you unplug the fridge, it no longer stays cool.

6. °C x 9/5 + 32 = °F (°F - 32) x 5/9 = °C °C + 273 = K

7. Liquid pumped into the cooling unit It is forced through tiny openings causing it to evaporate and draws heat from its surroundings. The gas is directed outside the cooling unit to the coils on the back. The gas condenses, releasing its heat to the surrounding air (outside the refrigerator)

8. Energy is Needed for a Phase Change  Whenever a substance changes phase, an energy transfer occurs. ○ Heat of Fusion: amount of energy needed to change a substance from a solid to a liquid (melt) ○ Heat of Vaporization: amount of energy required to change a substance from a liquid to a gas (boil) Solid Liquid Gas Energy is absorbed when change of phase is in this direction Energy is released when change of phase is in this direction

9. Practice Problems: The heat of fusion of water is 335 kj/kg.  Is energy absorbed or released when ice melts?  How much energy must be absorbed to melt 1 kg of ice? 335 kj  Is energy absorbed or released when water freezes?  How much energy must be released to freeze the water back into ice? 335 kj

10. There is no temperature change during a phase change! Energy is going into the change in phase not into eating up the substance!