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Thermal Physics

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  1. Thermal Physics

  2. HEAT AND TEMPERATURE

  3. Temperature • Temperature: A measure of how hot (or cold) something is • Specifically, a measure of the average kinetic energy of the particles in an object.

  4. If two objects of different temperatures are place in contact with one another, heat will “flow” from the high temp object to the low temp object. • Temperature is a property that determines the direction of thermal energy transfer between two bodies in thermal contact. • This flow of thermal energy will continue until the system reaches thermal equilibrium.

  5. Concept Check • What is the relationship between the temperature of a substance and the speed of its molecules? • High temperature = _____ KE (high or low)?

  6. Thermometers • Thermometer: an instrument that measures and indicates temperature a. b. c. Bimetallic strip

  7. Temperature Scales • Kelvin • International System (SI) of measurement • Fahrenheit • Celsius • Rankine • Newton • Romer scale

  8. Kelvin and Absolute Zero • The Kelvin scale is based on absolute zero • Absolute Zero: the temp at which molecular movement stops • 0 K on the Kelvin scale = -273.16ºC • It is the lowest temperature that can be theoretically achieved. • Scottish physicist William Thomson (a.k.a. Lord Kelvin) in 1848

  9. Absolute Zero

  10. Temperatures expressed by the Fahrenheit scale can be converted to the Celsius scale equivalent using the equation below: °C = (°F - 32°)/1.8 • Similarly, temperatures expressed by the Celsius scale can be converted to the Fahrenheit scale equivalent using the equation below: °F= 1.8•°C + 32°

  11. What is heat? • Heat: the transfer of energy between objects that are at different temperatures. • All matter has heat. • Measured in JOULES

  12. Measuring Heat Flow • Two Common Units • Joule • calorie • 4.184 J = 1 cal • 1Calorie = 1 kilocal = 1000 cal

  13. Heating and Cooling • If an object has become hotter, it means that it has gained heat energy. • If an object cools down, it means it has lost energy

  14. Endothermic and Exothermic Processes HEAT • Endothermic Process – heat is absorbed from the surroundings • Endo = Into

  15. Endothermic and Exothermic Processes HEAT • Exothermic process – heat is released into the surroundings • Exo = Exit

  16. Heating and Cooling cont… • Heat energy always moves from:HOT object COOLER object ex1. Cup of water at 20 °C in a room at 30°C - gains heat energy and heats up – its temperature rises ex2. Cup of water at 20 °C in a room at 10°C loses heat energy and cools down – its temperature will fall.

  17. ARE HEAT AND TEMP THE SAME THING? • NO….although the two quantities are related.Example: a beaker of water at 60 °C is hotter than a bath of water at 40 °C BUT the bath contains more joules of heat energy

  18. Review • What is the difference between heat and temperature? • HEAT is energy that transfers from one object/substance to another • TEMPERATURE is a measure of the amount of energy an object/substance has (how quickly the molecules are moving around)

  19. Internal energy • Internal energy is the total potential energy and random kinetic energy of the molecules of the substance. • Microscopic scale, temp is the average kinetic energy per molecule associated with thermal motions. • aka: the faster the molecule are vibrating or moving inside an object the more internal energy it possesses. • Two rocks in an oven. • Same heat input, different temperature rise. • Internal energy = total potential + total kinetic

  20. Copper Phases – Vapor (gas)

  21. Three Phases

  22. Copper Phases - Solid

  23. Copper Phases - Liquid

  24. Copper Phases – Vapor (gas)

  25. Measuring Heat Flow • Two Common Units • Joule • calorie • 4.184 J = 1 cal • 1Calorie = 1 kilocal = 1000 cal

  26. Concept Check • What causes heat to flow?

  27. Energy Transfer • The transfer of heat is normally from a high temperature object to a lower temperature object.

  28. 1) Conduction • Thermal Conduction: the transfer of heat within a substance, molecule by molecule.

  29. 2) Convection • Convection: the movement of matter due to the differences in density that are caused by temp. variations applet

  30. 3) Radiation • Radiation: the energy that is transferred as electromagnetic waves, Doesn’t need matter • Most radiation comes from the sun

  31. Conductor vs. Insulator • Conductor: any material through which energy can be transferred as heat • Insulator: poor conductors

  32. Now to a mole!

  33. Now to a mole! • Is a counting unit • The mole (mol) is the SI unit used to measure the amount of a substance. • It is based on the number of atoms in 12g of carbon • We can convert number of particles to moles and moles to particles.

  34. The Mole • is 6.02 X 1023 (in scientific notation) • Similar to a dozen, except instead of 12, it’s 602 billion trillion 602,000,000,000,000,000,000,000 • This number is named in honor of Amedeo Avogadro(1776-1856) • He studied quantities of gases and discovered that no matter what the gas was, there were the same number of molecules present

  35. What is a mole? • One mole of anything consist of 6.02x1023 units of that substance. • How many eggs are in a mole of eggs? • How many paper clips are in a mole of paper clips? • How many shoes are in a mole of shoes? Answer: 6.02x1023 eggs, paper clips, shoes

  36. Avogadro’s Number as Conversion Factor 6.02 x 1023 particles 1 mole or 1 mole 6.02 x 1023 particles Note that a particle could be an atom, a molecule or anything!!!

  37. Just How Big is a Mole? • Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles. • If you had Avogadro's number of unpoppedpopcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles. • If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

  38. The Mole This photograph shows one mole of salt(NaCl), water(H2O), and nitrogen gas(N2).

  39. We also know… • 1 mole of an elements atoms = that element’s average atomic mass (expressed in g)

  40. We also know… • Ex. 200.6g of Hg has 6.02x1023 atoms or 200.6g of Hg has 1 mol of Hg atoms • Conversion factor: 200.6g Hg/1 mol Hg • Ex. 32.07g of S has 6.02x1023 atoms or 32.07g of S has 1 mol of S atoms • Conversion factor: 32.07g S/1 mol S

  41. Example • We have an unknown # of H atoms. • We want to know many H atoms are present? • We weigh the sample, results = .5g

  42. Example • So .5g H X (1mol H/1.008g H) = .496 mol of H in the sample. • Then .496 mol H atoms X (6.022x1023 H atoms/1 mol H atoms) = 2.99x1023 H atoms in the sample

  43. Example • Convert 38g of P into moles of atoms • Convert 1.25 mol of Ag into # of atoms

  44. Practice • Convert 10g of Al into moles of atoms • Convert 8g of S into moles of atoms • Convert 25g of Ca into moles of atoms • Convert .371 mol Al into # of atoms • Convert .249 mol S into # of atoms • Convert .624 molCa into # of atoms

  45. Practice • Convert .371 mol Al into # of atoms • Convert .249 mol S into # of atoms • Convert .624 molCa into # of atoms

  46. Homework • 8 moles F = ? grams F • 4.2 moles Si = ? grams Si • 9.3 moles Mg = ? grams Mg • 945,000 Na atoms = ? moles Na • 74,000 Cl atoms = ? Moles Cl

  47. Summary • 1 amu = 1.66 x 10-24g • 1 ___ atom = _____ amu • 1 C atom = 12.01 amu • 1 Si atom = 28.09 amu • 1 mol of ___ = 6.022x1023 ____ units • 1 mol F = 6.022x1023 F atom • 1 mol Mg = 6.022x1023 Mg atom • What are the conversion factors?

  48. Summary • 1mol of ___ = “atomic/molar mass” g of _____ • 1mol Hg = 200.6g Hg • 1mol Cl = 35.45g Cl • “Atomic/molar mass” g of __ = 6.022x1023 atoms of ___ • 200.6g Hg = 6.022x1023 atoms Hg • 35.45g Cl = 6.022x1023 atoms Cl • What are the conversion factors?