1. Exothermic vs. Endothermic Reactions
Heat Transfer
Exothermic vs. Endothermic Reactions

2. Types of Reactions
Endothermic Reactions: Reactions that require an input of heat. These processes absorb energy (usually heat) from the surrounding environment.
Endo = Enter, Therm = Temperature/Heat
Exothermic Reactions:

3. Types of Reactions
Endothermic Reactions: Reactions that require an input of heat. These processes absorb energy (usually heat) from the surrounding environment.
Endo = Enter, Therm = Temperature/Heat
Exothermic Reactions: Reactions that release energy via heat or light.
Exo = Exit, Therm = Temperature/Heat

4. Methods of Heat Transfer

5. Methods of Heat Transfer
Convection: Heat transfer through the movement of fluids based on their densities. More dense liquids sink, less dense liquids rise.

6. Methods of Heat Transfer
Conduction: Heat transfer through direct contact to a heat source.

7. What makes a substance a good…
Conductor?
Insulator?
Electric currents can flow freely.
Contains atoms with loosely bound electrons.
Ex: Metals
Electric currents have difficulty flowing.
Contains atoms with tightly held electrons.
Ex: Nonmetals

8. Good Conductors: Metals

9. Methods of Heat Transfer
Radiation: Heat transfer through the emission electromagnetic waves from a heat source that travel through transparent spaces (air).

10. What makes a substance a good radiator?
Good radiators are good absorbers.
Poor radiators are poor absorbers.

11. What is the difference between an absorber and a reflector?
Good Absorber
Good Reflector
Able to absorb different colors and types of electromagnetic waves.
Ex:
Black objects absorb all wavelengths of visible light.
Dull surfaces
Unable to absorb many different colors or types of electromagnetic waves.
Ex:
White objects reflect all wavelengths of visible light.
Shiny surfaces

12. Absorbers vs. Reflectors

13. Specific Heat
Specific Heat: A measure of the amount of heat required to raise the temperature of 1 gram of a substance 1 oC.
Units: Joules (J) – amount of work required to lift 100 grams,1 meter from the ground.

14. The greater the specific heat…
The more thermal energy required to raise its temperature.
Specific Heat of Water = J/g oC
So, it takes J of thermal energy to raise 1 g of water 1 oC.
The more thermal energy it has compared to other materials with the same mass and temperature.

15. Comprehension Check #1:
Specific Heat of Iron: J/g oC
Specific Heat of Water: J/g oC
If I take 1 gram of each substance, which will raise 1oC faster? Why?

16. Comprehension Check:
Desert Daytime Temperature: oF
Desert Nighttime Temperature: oF
Commack Daytime Temperature: oF
Commack Nighttime Temperature: 46 oF
Why does the temperature vary so little on Long Island throughout the day compared to the desert?
Temp. Difference: 31 oF
Temp. Difference: 5 oF