Temperature and Thermal Energy thermodynamics: the study of heat caloric theory: early theory of TE honolulu.hawaii.edu An incorrect theory which serves as a model for scientific growth anguage retains vestiges of concept heat flows, objects soak up heat leads to confusion: we speak of it as a substance while told that it is not metaphor Lavoisier coined the term later in 1787 firmly entrenched by 1780 largely discredited by 1850 conservation of heat was a basic premise heat lost by one object is gained by another this is true and still a basis for calorimetry heat was thought of as a substance fluid = can flow a fluid called caloric Properties of Caloric could not be created nor destroyed all substances contain caloric and absorb or release it flows from hot to cold objects or substances counterbalanced attractive forces of "particles of matter" self repulsion caused it to flow from higher to lower concentration kind of like pressure in a balloon state of matter determined by amount of caloric caloric surrounds the particles of matter causing them to swell caloric occupied space, so gas has lots of caloric Kinetic Molecular Theory 1) All matter is made up of particles in constant motion with elastic collisions (KE = KE') 2) The: >motion >KE > Temperature bonds: electromagnetic forces particles vibrate back and forth (KE) intermolecular bond resist vibration, therefore particles have PE (elastic/electric) overall energy is called Thermal Energy http://hyperphysics.phy astr.gsu.edu/hbase/acloc.html atomic clock 1
Temperature: measures "hotness" of an object. Temperature is a measure of the average energy (KE) of the particles of an object. https://www.youtube.com/watch?v=v12xg80kczw https://www.youtube.com/watch?v=dhjmoh38agy states of water http://mc2.cchem.berkeley.edu/java/molecules/index.html http://lectureonline.cl.msu.edu/~mmp/kap10/cd283.htm Thermal Energy: total PE + KE associated with the random motion and arrangement of the particles of a material (Total Internal Energy) Heat: Thermal Energy that's absorbed, given up, or transferred from one body to another. Flowing of TE (thermal contact) Temperature: physical quantity that is proportionate to the average (translational) KE of the particles in matter. a measure of a body's ability to give up or absorb TE from another body 2
Can't measure KE (motion) directly, so we measure its effect on something else. (indirect measurement) > temp >motion > volume > temp >volume > temp > electrical resistance to current > temp > resistance Temperature Scales Fahrenheit based on body temperature/brine (Rankine) Celsius based on freezing and boiling of water Kelvin based on "absolute zero" http://en.wikipedia.org/wiki/fahrenheit http://en.wikipedia.org/wiki/celcius http://en.wikipedia.org/wiki/absolute_zero C = (F 32) /1.8 or 5/9(F 32) F = (C x 1.8) + 32 or 9/5C + 32 K = C + 273 3
When converting between C and F 180 is the magic number using boiling of water F C C = 5/9(F 32) or (F 32) /1.8 212 o F = o C 212 o F 32 = 180 180/1.8 = 100 o C C F F = 9/5C + 32 or (C x 1.8) + 32 100 o C= o F 100 o C x 1.8 = 180 180 + 32 = 212 o F 10 0 F = 0 C 28 0 C = 0 F 4
10 0 F = 0 C C = (F 32) /1.8 C = (10 0 F 32)/1.8 C = 12 0 C 28 0 C = 0 F F = (C x 1.8) + 32 F = (28 0 C x 1.8) + 32 F = 82 0 F 82 0 F = 0 C 38 0 C = 0 F 5
82 0 F = 0 C C = (F 32) /1.8 C = (82 0 F 32)/1.8 C = 28 0 C 38 0 C = 0 F F = (C x 1.8) + 32 F = (38 0 C x 1.8) + 32 F = 100 0 F 52 0 F = 0 C 88 0 C = 0 F 6
52 0 F = 0 C C = (F 32) /1.8 C = (52 0 F 32)/1.8 C = 11 0 C 88 0 C = 0 F F = (C x 1.8) + 32 F = (88 0 C x 1.8) + 32 F = 190 0 F Thermal Energy Transfer conduction convection radiation 7
conduction If you put a metal bar into a flame, it gets hot quickly. Soon you can't hold it. If you put a glass bar into a candle, it won't get too hot to hold. But if you touched the end that was in the flame, you would find that it was really hot! The process in which heat passes through a solid substance is called conduction. Metals are good conductors of heat. Non metals are generally bad conductors of heat. Liquids and gases are bad conductors of heat as well. A bad conductor of heat is called an insulator. Your quilt, or winter jacket, traps air which is a good insulator. Convection Convection occurs only in liquids and gases. We call liquids and gases fluids. It cannot happen in solids. It needs particles to be free to move about. When a liquid is heated, the molecules at the bottom move about with bigger vibrations. They take up more space which means that the density goes down. The less dense fluid rises. It gives its energy to the fluid above, and cools down. It becomes denser and falls back to the bottom. A convection current is set up. 8
"hot" plate Radiation Radiation passes heat on as an electromagnetic wave called infra red radiation. All the heat from the Sun reaches us as electromagnetic radiation. Our eyes cannot see infra red, but a digital camera can. Here is a picture of a hot plate that appears much brighter than it actually is because of the infra red radiation. E = W = Fd thermal energy KE = ½mv 2 PE = mgh Q = mcδt "g" is unique to superior object... [ g = Gm 1 /r 2 ] all object attract all other objects and each has their own "g" value "c" is unique to molecular/ atomic make up of an object... [ c = Q/m t ] all object Note the similarities to the other forms of energy!!!!... amounts... unique properties of that form of energy... what's changing... mass g or c v, h, or t 9
Q = mcδt Specific Heat specific heat "thermal property of matter" c = Q/mΔt c = J/(kg 0 C) TE kg 1 0 C "c" is the thermal energy needed to change l kg of a substance 1 degree C How much TE does it take to raise 100.g of iron from 17 0 C to 100. o C? TE =? m i = 100 g 0.100 kg t 1 = 17 0 C t 2 = 100 0 C iron 10
How much TE does it take to raise 100.g of iron from 17 0 C to 100. o C? TE =? (Q) m i = 100 g 0.100 kg t 1 = 17 0 C t 2 = 100 0 C Q = mcδt Q = mc(t f t i ) Q =.100 kg[450 J/(kg 0 C)](100. 0 C 17 0 C) Q =.100 kg[450 J/(kg 0 C)](100. 0 C 17 0 C) Q = 3700 J PE = mgh = (kg)m/s 2 (m) = N x m = J TE = Q = mcδt = kg[j/(kg 0 C)] 0 C = J c = Q/mΔt = J/(kg 0 C) some common "c" values text page 279 (each textbook will list slightly different values for "c" copper 385 J/kg 0 C H 2 0 4180 J/kg 0 C metal 450 J/kg 0 C lead 135 J/kg 0 C ice 2060 J/kg 0 C steam 2020 J/kg 0 C 11
100 0 C 60 0 C Law of Heat Exchange Q L + Q g = 0 Q lost + Q gained = 0 100 g of metal at 100.0C 100 g of H20 at 60 0 C mix them together! Steel loses TE because it's at a higher temperature Water gains TE because it's at a lower temperature t 100 0 C im Q L Temp 60 0 C t iw t fm t f thermal equilibrium t fw Q g t fm = f fw = t f Time remember the inelastic collision when v 1 ' = v 2 ' = v ' you mix: 100 g of steel at 100 0 C 100 g of water at 60 0 C What is the final temperature? Q L + Q g = 0 expand Δt's mcδt s + mcδt w = 0 dist. mc(t f t i ) s + mc(t f t i ) w = 0 (mct fs mct is ) + (mct fw mct iw ) =0 is t fs = t fw?...yes, t fs = t fw = t f mc s t f mct is + mc w t f mct iw =0 mc s t f + mc w t f = mct is + mct iw t f (mc s + mc w ) = mct is + mct iw t f = mct is + mct iw mc s + mc w add "mcti" 's from both sides factor out the "mc" 's divide by "mc" 's QLs = 1625 J steel Qgw = 1630 J water tf = 63.9 0 C t f =.1kg(450J/kgC)100 0 C +.1kg(4180J/kgC)60 0 C [.1kg(450J/kgC)] + [.1kg(4180J/kgC)] t f = 4500 J + 25100 J 463J/ 0 C t f = 63.9 0 C Q L + Q g = 0 mcδt s + mcδt w = 0 mc(t f t i ) s + mc(t f t i ) w = 0 [.1kg(450J/kgC)(63.9 0 C 100 0 C)] + [.1kg(4180J/kgC)(63.9 0 C 60 0 C)] = 0 note the " " denotes loss of TE 1625 J + 1630 J = 0 slightly off because of rounding and "+" denotes gain of TE 12
t is = 100 0 C 100 0 C steel QLs = 1625 J t iw = 60 0 C 60 0 C Q gw = 1630 J water t f = 63.9 0 C 13