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Heat and temperature
 

Heat and temperature

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Lesson taken from the book Science 7 of Phoenix Pub. House by Lilia G. Venco et.al, 2012.

Lesson taken from the book Science 7 of Phoenix Pub. House by Lilia G. Venco et.al, 2012.

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    Heat and temperature Heat and temperature Presentation Transcript

    • Heat andTemperature Prepared by: Victor R. Oribe
    • What is heat?Up to the middle of 19th century, it wasthought that heat was aninvisible, weightless substance calledCaloric Fluid.When wood, for instance is burned, it is hot because itproduces large quantities of caloric fluid which istransferred to other substance close by.The burned wood, having lost its caloric fluid, is saidto have cooled off.
    • The theory of Caloric Fluidwas disproved around 1800by Count BenjaminThompson Rumford, anAmerican-born physicist.Count Benjamin ThompsonRumford concluded thatheat was produced fromfriction alone.
    • It was only about 40 years later that an Englishphysicist, James Prescott Joule proved that ameasurable amount of mechanical energy couldalways be transformed into definite amounts of heat.He concluded that heatmust be just anotherform of energy.
    • Sources of Heat Natural Sources1. The Sun When the sun’s energy reaches the earth, 30% of its is immediately reflected back out into space. Only 70% remains to interact with the earth, and warm it up. Of the 70%, 20% is energy to heat both the surface of the earth, as well as the ocean.
    • It is the sun’s heatenergy that makesplants and animals toprovide themselveswith energy.These plants providefood for animals.Human eat plantsand animals toprovide themselveswith energy.Much of the heat on earth may be traced back to thesun.
    • 2. The interior of the EarthA great amount of heatalso comes from buried hotrocks and lava flow fromcraters and crevices oferupting volcanoes.The hot spring in Tiwi, Albay, Los Banos, Laguna andin Tayabas Quezon are proofs that the earth’s interior ismuch hotter than its surface.
    • Artificial Sources1. Chemical Action When fuels like coal, kerosene, wood, and gasoline are burned, they are used as artificial sources of heat. The oxygen we breathe in burns the food we eat, producing enough body heat to keep our body temperature close to 370 C.
    • 2. Mechanical Action Heat energy produced by a friction.
    • 3. Electrical Energy Electricity is a very common source of heat at home. Oven toaster and electric iron are heated by the resistance of the heating coils to the electricity passing through them.
    • 4. Nuclear Energy The tremendous amount of energy from nuclear reactions can be used to change water into steam, which is then used to operate a turbine to generate electricity.
    • How much have you learned?1. Heat is one of the topics in Thermodynamics. What is thermodynamics?2. Use kinetic molecular theory as a basis to explain how heat is produced.3. Solar energy is used by plants to manufacture their own food. Give two other examples how solar energy is used.4. Make a short description of the following kinds of thermometer: A. liquid-in-glass thermometer B. Platinum-resistance thermometer C. Thermocouple D. Optical E. thermograph
    • Temperature ScaleThe most common thermometer used in thelaboratory is the Mercury Thermometer.
    • Colored alcohol is another liquid commonly used inthermometer.
    • Celsius ScaleCommonly known as Centigrade ScaleThis scale was devised in1741 by a Swedishastronomer, AndersCelsius, based on theproperties of water.
    • On the Celsius scale, the freezing point ofwater is fixed at 0 degree Celsius (00 C)The boiling point of pure water undernormal atmospheric pressure, 760 mmHg (at sea level), is 100 degrees Celsius(1000 C).The normal temperature of the humanbody is 370 C
    • Fahrenheit ScaleThe Fahrenheit scale wasdevised by Daniel GabrielFahrenheit, A Germanphysicist.Unites States of America and England use theFahrenheit scale for weather observation and otherpurposes.
    • On Fahrenheit scale, 320 F isthe freezing point of water and2120 F is the boiling point.
    • Kelvin Scale or Absolute ZeroNamed after SirWilliam Thompson(Lord Kelvin) whodevised it.
    • This temperature scale is often used whengases are involved.Its zero point (0 K) corresponds to -2730 Cand is referred to as Absolute Zero or thetemperature at which the molecularenergy of matter is minimal.On the Kelvin scale, the freezing point ofwater is 273 K and the boiling point ofwater is 373 K.
    • To convert temperature readings fromone scale to another, the equation beloware used:
    • Converting Units of TemperatureoC to oF oF = (9/5)( oC) + 3238.7 oC oF oF = (1.8)(OC) + 32 = (1.8) (38.7) + 32 = 69.66 + 32 = 101.7
    • oF to oC oC = 5/9 ( oF – 32) 101.7 oF o C oC = 5/9 ( oF – 32) = .555 (101.7 – 32) = (.555) (69.7) = 38.7
    • oC to K K = 273 + oC 38.7 oC K K = 273 + oC = 273 + 38.7 = 311.7
    • Convert the following1) 37o C to oF 1) 98.6oF2) 350oF to oC 2) 176.7oC3) 100oC to K 3) 373 K4) 95o C to oF 4) 203 oF5) 130oF to K 5) 327.4 K6) 39oC to oF 6) 102 oF 7) -160oF to oC 7) -107oC 8) 80.0oF to oC 8) 27 o C 9) 27oC to K 9) 300 K10) 120oC to oF 10) 248 oF
    • How Heat is Measured?Thermometer only gives us an idea of the totalpotential energy and kinetic energy of the moleculesin an object.It does not tell us how much heat a particular objectabsorbs or gives off.In fact there is no instrument that directly measuresthe amount of heat energy that a body gives off orabsorbsIf you want to calculate the amount of heat given offby a piece of charcoal or a certain kind of gas, thenyou have to determine the change in temperature itproduces on a definite volume of water.
    • Units of HeatCommon units used for measuring heat energy: a. Calorie (cal) b. kilocalorie (kcal) c. joule (J)The SI unit for heat, as for any other form of energy isthe Joule (1 N.m = 1 joule)Today, the calorie is defined in terms of the joule: thatis 1 cal = 4.184 J.This is the mechanical equivalent of heat1 Kcal = 1000 calories
    • Effects of Heat1. Generally when a substance absorbs heat, itstemperature rises.2. Solid usually melt or change to the liquidstate when heated.
    • 3. Liquid may absorb enough energy whenheated to change to vapor state.
    • 4. Almost all objects expand when heated.
    • 5. A change in the heat content of a substancecan cause chemical changes.
    • 6. Heat causes many changes in bodilyfunctions of living organismsEnzymes are protein-like substances formed in humancells that act as catalysts in initiating or speeding upspecific chemical reactions.Each has a characteristics shape that allows it to holdtwo or more molecules close enough together so theycan react chemically.If the temperature is increased, then the speed ofmoving molecules is also increased.Bombardment by high speed molecules in the cell cancause the enzymes to lose its shape.It can no longer perform its vital function.
    • Two glasses stack together.If we twist them apart, one or bothof them may break.What is the safest way to separatethe two glasses that stick together?One way is to pour some cold waterinto the inner glass and dip theouter glass in hot water.Within a short while, the two glasses can easily bepulled apart.Why? Generally most substances expands when heated and contract when cooled.
    • A change in temperature producesa change in length in almost allsolid.Experimental results have shownthat change in length is directlyproportional to change intemperature and to the originallength of the object.Different solids of the same lengthdiffer in their expansion for thesame change in temperature.
    • In liquids the effect of heat is an increase in theirvolume while the effect of cooling is a decrease in theirvolume.
    • Expansion of Gases Why do gases expand at a greater rate than solids and liquids?
    • Change of PhaseWhenever the temperature of a substancechanges, there is an accompanying change in itsmolecular structure.If the change in molecular structure is such that itbecomes noticeable, then we say that the substanceis undergoing a Change of Phase.
    • Heat TransferHeat may be transferred inthree ways: a. Conduction b. Convection c. Radiation
    • a. Conduction Transmission of heat from particle to particle Conduction of heat in an object will take place only when one part of the object has a higher temperature than another part.The part with a highertemperature will transfer itsheat energy to that partwith a lower temperature.
    • Solid are the best conductors of heat.Among solids, metal conduct heatthe best.But metals differ in theirconductivity.Silver is very good conductor of heatthan iron and lead. Why?
    • b. Convection The heat energy is distributed by the liquid or gaseous molecules in circling currents.
    • c. Radiation Transfer of heat through electromagnetic waves.
    • 2 13 4
    • QUIZ
    • 1. The absolute zero temperature is _____ a. -273 0 C b. -320 C c. 00 C d. 273 K
    • 2. The space between the walls ofthe double-walled thermos bottleis evacuated to ______ a. increase volume b. reduce convection c. reduce heat transfer by conduction d. both b and c
    • 3. Dry ice has a temperature of -110.2 0 F. What would itstemperature be on the Celsiusscale? a. -7110 C b. -198.3 0 C c. -142.2 0C d. -79 0C
    • 4. Room temperature is often 0identified as 68 F. Whattemperature is this on the Kelvinscale? a. 20 K b. 100 K c. 293 K d. 341 K
    • 5. The transfer of energy from asource to an object by directcontact between them is _____ a. conduction b. convection c. insulation d. radiation
    • 6. As more heat is added to asample of water boiling in astove, its temperature ______ a. decreases b. increases c. increases then decreases d. remains the same
    • 7. When water reaches 4 0 C, ____. a. it will expand only if heated. b. its volume will remain constant. c. it will expand whether it is cooled or heated. d. it will contract until it freezes into ice, and then expand.
    • 8. When does vaporizationhappen? It _____________. a. will occur only at night. b. takes place at very great pressures. c. occurs at the boiling point temperature d. takes only at a definite temperature may occur at a definite temperature or at any temperature.
    • 9. Which of the followingstatements is true about boiling?It ____________. a. is lower than evaporation. b. takes place at a definite temperature. c. is the same for all liquids at the same temperature. d. takes place when bubbles begin to appear in the liquid.
    • 10. The rate of evaporation maybe increase by _______ a. raising the temperature of the liquid. b. increasing the surface area of the liquid. c. decreasing the air pressure on the surface of the liquid. d. any of the above.
    • 11. What is condensation? It ____ a. is an exothermic process. b. is the opposite process of melting. c. is due to the increase in the kinetic energy of the particle of the liquid. d. refers to the change from solid state to gaseous state form of matter.
    • Two cars of the same model, the same brand, and thesame size, are both locked and parked under the sunin an open parking lot. The two cars are parkedfrom 9:00 A.M. to 5:00 P.M. One of the cars is ivorywhite in color and the other is dark blue.12. Under the same condition, at 12:00 noon, _____ a. the dark-colored will be hotter inside. b. the ivory-colored car will be hotter inside. c. since both are locked, the sun will not affect either car. d. since both are under the same sun, they will both be equally hot.
    • Match Column A with Column B Column A Column A_____13. William Thompson a. Centigrade tempt. Scale_____14. Anders Celsius b. Absolute Tempt. Scale_____15. D. Gabriel Fahrenheit c. Fahrenheit Tempt. Scale_____16. B.T. Rumford_____17. J. Prescott Joule d. Heat is produced by friction e. Concluded that heat is a form of energy.
    • 18-21. Enumerate the differentartificial sources of heat. 18. 19. 20. 21.
    • 22-24. Enumerate the differentmethods of heat transfer. 22. 23. 24.
    • 25. True or False Land breeze and sea breezeoccurs because of conviction current.
    • Answer
    • 1. The absolute zero temperature is _____ a. -273 0 C b. -320 C c. 00 C d. 273 K
    • 2. The space between the walls of thedouble-walled thermos bottle isevacuated to ______ a. increase volume b. reduce convection c. reduce heat transfer by conduction d. both b and c
    • 3. Dry ice has a temperature of -110.20 F. What would its temperature beon the Celsius scale? a. -7110 C b. -198.3 0 C c. -142.20 C d. -79 0C
    • 4. Room temperature is often 0identified as 68 F. Whattemperature is this on the Kelvinscale? a. 20 K b. 100 K c. 293 K d. 341 K
    • 5. The transfer of energy from asource to an object by directcontact between them is _____ a. conduction b. convection c. insulation d. radiation
    • 6. As more heat is added to asample of water boiling in astove, its temperature ______ a. decreases b. increases c. increases then decreases d. remains the same
    • 7. When water reaches 4 0 C, ____. a. it will expand only if heated. b. its volume will remain constant. c. it will expand whether it is cooled or heated. d. it will contract until it freezes into ice, and then expand.
    • 8. When does vaporizationhappen? It _____________. a. will occur only at night. b. takes place at very great pressures. c. occurs at the boiling point temperature d. takes only at a definite temperature may occur at a definite temperature or at any temperature.