Physical Science Chapter 5 Cont3. Temperature & Heat

Transcription

1 Physical Science Chapter 5 Cont3 Temperature & Heat

2 What are we going to study? Heat Transfer Phases of Matter The Kinetic Theory of Gases Thermodynamics

3 Specific Heat (Capacity) Specific Heat Latent Heat (phase changes) of Fusion Of Vaporization Section 5.3

4 Specific Heat (Capacity) Specific Heat Latent Heat (phase changes) of Fusion Of Vaporization Section 5.3

5 Graph of Temperature vs. Heat for Water Latent heat of fusion heat necessary to go from A to B Latent heat of vaporization heat necessary to go from C to D 5 5 Section 5.3

6 Pressure affects Phase Changes Increase pressures at lower altitudes increase boiling point Pressure cooker higher pressure leads to higher boiling point that allows a higher temperature that cooks the food faster! 5 6 Section 5.3

7 Evaporation Cooling due to D Phase In order for water to undergo a phase change from liquid to gas the molecules of water must acquire the necessary amount of heat (latent heat of vaporization) from somewhere. In the case of sweat evaporating, some of this heat comes from a person s body, therefore serving to cool the person s body! More evaporation occurs in dry climates than in humid climates resulting in more cooling in dry climates. Section 5.3

8 PHASE CHANGES Description of Phase Change Solid to liquid Liquid to solid Term for Phase Change Melting Freezing Heat Movement During Phase Change Heat goes into the solid as it melts. Heat leaves the liquid as it freezes.

9 PHASE CHANGES Description of Phase Change Liquid to gas Term for Phase Change Vaporization, which includes boiling and evaporation Gas to liquid Condensation Solid to gas Sublimation Heat Movement During Phase Change Heat goes into the liquid as it vaporizes. Heat leaves the gas as it condenses. Heat goes into the solid as it sublimates.

10 Heat Transfer Occurs by Conduction Convection Radiation 5 10 Section 5.4

11 Conduction Conduction is the transfer of heat by molecular collisions. How well a substance conducts depends on the molecular bonding. Liquids/gases generally poor thermal conductors (thermal insulators) Metals generally good thermal conductors Section 5.4

12 Convection Convection is the transfer of heat by the movement of a substance, or mass, from one position to another Section 5.4

13 Radiation Radiation is the process of transferring energy by means of electromagnetic waves. Electromagnetic waves carry energy even through a vacuum. WtK6vc 5 13 Section 5.4

14 Radiation In general dark objects absorb radiation well and light colored objects do not absorb radiation well Section 5.4

15 Insulation Good insulating material generally has an abundance of open air space to inhibit the movement of heat. Goose down sleeping bags Styrofoam House insulation (spun fiberglass) Pot holders (fabric with batting) Double paned windows void between glass panes 5 15 Section 5.4

16 A vacuum bottle Incorporates principles of all three methods of heat transfer to help prevent the transfer of heat energy Section 5.4

17 A Vacuum (thermos) Bottle Partial vacuum between the double walls minimizes the conduction and convection of heat energy. The silvered inner surface of the inner glass container minimizes heat transfer by radiation. Thus, a quality vacuum (thermos) bottle is designed to either keep cold foods cold or hot foods hot Section 5.4

18 STATES OF MATTER The Four States of Matter Solid Liquid Gas Plasma

19 Kinetic Theory of Matter Matter is made up of particles which are in continual random motion.

20 STATES OF MATTER SOLIDS Particles of solids are tightly packed, vibrating about a fixed position. Solids have a definite shape and a definite volume. Heat

21 STATES OF MATTER LIQUID Particles of liquids are tightly packed, but are far enough apart to slide over one another. Liquids have an indefinite shape and a definite volume. Heat

22 STATES OF MATTER Particles of gases are very far apart and move freely. GAS Gases have an indefinite shape and an indefinite volume. Heat

23 But what happens if you raise the temperature to super-high levels between 1000 C and 1,000,000,000 C? Will everything just be a gas?

24 STATES OF MATTER PLASMA A plasma is an ionized gas. A plasma is a very good conductor of electricity and is affected by magnetic fields. Plasmas, like gases have an indefinite shape and an indefinite volume. Plasma is the common state of matter

25 STATES OF MATTER SOLID LIQUID GAS PLASMA Tightly packed, in a regular pattern Vibrate, but do not move from place to place Close together with no regular arrangement. Vibrate, move about, and slide past each other Well separated with no regular arrangement. Vibrate and move freely at high speeds Has no definite volume or shape and is composed of electrical charged particles

26 Some places where plasmas are found 1. Flames

27 2. Lightning

28 3. Aurora (Northern Lights)

29 The Sun is an example of a star in its plasma state

30 Kinetic Theory of Gases A gas consists of molecules moving independently in all directions at high speeds. The higher the temperature the higher the average speed of the molecules. The gas molecules collide with each other and the walls of the container. The distance between molecules is, on average, large when compared to the size of the molecules Section 5.6

31 Pressure (Gas) The result of the collisions of billions of gas molecules on the wall of a container (a balloon or ball for example) more gas molecules more collisions more force on the container therefore more pressure 5 31 Section 5.6

32 Pressure Pressure is defined as force per unit area. p = F/A SI Unit = N/m 2 = pascal (Pa) Common Unit = atmosphere 1 atm = normal atmospheric pressure at sea level and 0 o C 1 atm = 1.01 X 10 5 Pa = 14.7 lb/in 2 Force, Pressure, Area Illustrated As the (A) decreases, (p) increases 5 32 Section 5.6

33 Factors affecting the Pressure of a Confined Gas (Ideal Gas Law) P a NT V N must be constant for this equation to be valid 5 33 Section 5.6

34 Thermodynamics Deals with the dynamics of heat and the conversion of heat to work. (car engines, refrigerators, etc.) First Law of Thermodynamics heat added to a closed system goes into the internal energy of the system and/or doing work H = DE i + W H = heat added to a system (1st Law of Thermodynamics) DE i = change in internal energy of system W = work done by system 5 34 Section 5.7

35 Second Law of Thermodynamics It is impossible for heat to flow spontaneously from a colder body to a hotter body No heat engine operating in a cycle can convert all thermal energy into work. (100% thermal efficiency is impossible.) 5 35 Section 5.7

36 Third Law of Thermodynamics It is impossible to attain a temperature of absolute zero. Absolute zero is the lower limit of temperature Section 5.7

37 Entropy The change in entropy indicates whether or not a process can take place naturally. Entropy is associated with the second law. Entropy is a measure of the disorder of a system. Most natural processes lead to an increase in disorder. (Entropy increases.) Energy must be expended to decrease entropy. Since heat naturally flows from high to low, the entire universe should eventually cool down to a final common temperature Section 5.7

38 Pressure How air conditioner work