1. Heat Part 2

2. Heat
Phase change - the process of a substance changing from a solid, liquid, or gas to a solid, liquid, or gas
Examples include: melting, vaporizing, solidification (freezing), condensing, deposition, and sublimation

3. Heat
Deposition - when a substance goes from a vapor to a solid without the liquid phase in between
Frost on your windshield
Sublimation - when a substance goes from a solid to a vapor without the liquid phase in between
Dry ice

4. Heat
While a substance is going through a phase change the temperature remains constant
The substance still absorbs energy even though the temperature is not changing

5. Heat
Melting point - the temperature where a solid changes into a liquid.
The temperature stays constant until all the solid has turned to liquid
Heat of fusion - the amount of heat (J)required to change one kg of solid into liquid

6. Heat Boiling point - the temperature where a liquid changes into a gas
The temperature stays constant until all the liquid has changed into a gas
Heat of vaporization - the amount of heat (J) required to change one kg of a substance from a liquid to a solid

7. Heat
Latent heat - the heat of fusion or heat of vaporization required for phase changes
Temperatures of substances do not change during latent heating
They just undergo a phase change
Values can be looked up or experimentally determined

8. Heat
Example 2:
How much heat energy is required to change a 5 kg block of ice (-20°C) to a vapor (120°C)? The latent heats of fusion and vaporization are 3.33 x 105 J/kg and 22.6 x 105 J/kg.

9. Heat
Methods of heat transfer
Conduction
Convection
Radiation

10. Heat Conduction - Heat transfer when materials are in direct contact
Conductors - materials that transfer heat very well (metals)
Insulators - material that do not transfer heat well (plastic)
Conduction usually occurs between two solids
Energy moves but the molecules do not

11. Heat Convection - heat transfer where the molecules move
Usually occurs in fluids (liquids and gases)
Warmer molecules become less dense and buoy upward to spread out
They are replaced by cooler molecules that can then be heated

12. Heat Convection is responsible for our weather
Convection is also what causes plate tectonics (the movement of the Earth’s crust over the mantle)

13. Heat
Radiation - a means of heat transfer that does not involve molecules (the energy can travel through a vacuum)
Radiation is energy traveling on waves
Does not require direct contact like conduction
Molecules do not move like conduction

14. Heat
Ultimately the energy we have here on Earth came to us through radiation from the sun
Throughout the day the Earth absorbs energy from the sun
At night the Earth radiates the energy outward

15. Heat
Objects that are darker in color tend to absorb more radiant energy
Objects that are lighter in color tend to reflect more radiant energy
A good absorber (take in) of radiant energy is also a good emitter (give away) of radiant energy

16. Heat Radiation is the culprit in “global warming”
Radiation from the sun is absorbed, but due to green house gases the radiation cannot escape, thus the average kinetic energy (temperature) rises
The reduction in the polar ice caps also reduces Earth’s ability to reflect the sun’s radiation