Temperature Thermal Expansion Ideal Gas Law Kinetic Theory Heat Heat Transfer Phase Changes Specific Heat Calorimetry

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2 Temperature Thermal Expansion Ideal Gas Law Kinetic Theory Heat Heat Transfer Phase Changes Specific Heat Calorimetry

3 Zeroeth Law Two systems individually in thermal equilibrium with a third system (such as a thermometer) are in thermal equilibrium with each other. That is, there is no flow of heat within a system in thermal equilibrium

4 1st Law of Thermo The change of internal energy of a system due to a temperature or phase change is given by (next chapter): Temperature Change: Q = mct Phase Change: Q = ml Q is positive when the system GAINS heat and negative when it LOSES heat.

5 2nd Law of Thermo Heat flows spontaneously from a substance at a higher temperature to a substance at a lower temperature and does not flow spontaneously in the reverse direction. Heat flows from hot to cold. Alternative: Irreversible processes must have an increase in Entropy; Reversible processes have no change in Entropy. Entropy is a measure of disorder in a system

6 3rd Law of Thermo It is not possible to lower the temperature of any system to absolute zero.

7 Temperature is measured by a thermometer. Kelvin is the Absolute Scale. 9 T( F) T( C) T( C) T ( F) 32 9 T( K) T( C)

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9 What is "room temperature" (68 degrees F) in Celsius and Kelvin? 5 T( C) T ( F) C T( K) T( C) K Do book quiz 2!

10 30 is HOT. 20 is NICE. 10 is CHILLY. Zero is ICE!

11 Thermal Expansion of Solids: Linear L L T Coefficients determined experimentally! 0

12 Thermal Expansion: Volume V V T ~ 3 0

13 Thermal Expansion: Linear

14 Thermal Expansion: Linear The coefficient of linear expansion of steel is 12 x 10-6 / C. A railroad track is made of individual rails of steel 1.0 km in length. By what length would these rails change between a cold day when the temperature is -10 C and a hot day at 30 C? L L T 6 3 L (12 x10 / C)(10 m)(30 C ( 10 C)) 0 L.48m

15 L L T What change in temperature is needed to fill the gap, 1.3 x 10-3 m? 0 brass 19x10 C 23x10 C AL 3 Lbrass LAl 1.3x10 m 3 1.3x10 m T L L brass brass Al Al C

16 Thermal Expansion When the temperature of a metal ring increases, does the hole become larger? Smaller? Or stay same?

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18 Circle Expansion The coefficient of linear expansion of aluminum is 23 x 10-6 /C. A circular hole in an aluminum plate is cm in diameter at 0 C. What is the diameter of the hole if the temperature of the plate is raised to 100 C? L L T 0 6 (23x10 / C)(2.725 cm)100 C 6.3x10 3 cm d 2.731cm

19 Fluids: Liquids & Gases Fluids are substances that are free to flow. Atoms and molecules are free to move. They take the shape of their containers. Cannot withstand or exert shearing forces. Liquids: Incompressible (density constant) Gases: Compressible (density depends on pressure) Parameters to describe Fluids: Density: = mass/volume Pressure: P = Force/Area [P] = N/m 2 = 1 Pascal (Pa)

20 Liquid Units There are 1000 liters in 1 cubic meter! 1 liter = 10-3 m 3 = 10 3 cm 3 1 liter of water has a mass of 1 kg and a weight of 9.8N. 1kg 1000kg H2 0 liter m 3

21 Density Density of C: water = 1g/cm 3 = 1000 kg/m 3 = 1kg/liter Density of 0 C: m V Air = 1.29x10-3 g/cm 3 = 1.29 kg/m 3 Density depends on temperature! Most substances EXPAND upon heating. How does that change their densities? m V m V REDUCES DENSITY!

22 Water: The Exception C: water =1000 kg/m 3 0 C: ice = 917 kg/m 3

23 Increasing the Pressure Does increasing the external pressure increase or decrease the boiling temperature of water? Increases! Boiling happens when vapor pressure in the liquid exceeds the external vapor pressure - now greater due to the increased pressure so the boiling temperature increases!

24 The absolute Pressure P of an ideal gas is directly proportional to the absolute (Kelvin) temperature T and the number of moles n of the gas and inversely proportional to the volume V of the gas: P V = nrt n = # moles R = 8.31 J/(mol-K) Universal Gas Constant

25 Thermometer, Liquid in Glass A common type of thermometer is a liquid-in-glass The material in the capillary tube expands as it is heated The liquid is usually mercury or alcohol

26 Barometers Measuring Air Pressure Fluid in the tube adjusts until the weight of the fluid column balances the atmospheric force exerted on the reservoir. 10.3m Not to Scale!!! Mercury Barometer atm x Pa Water Barometer 760mm

27 The Atmosphere At sea level, the atmosphere has a density of about 1.29 kg/m 3. The average density up to 120 km is about 8.59 x10-2 kg/m 3.

28 The Atmosphere A square meter extending up through the atmosphere has a mass of about 10,000 kg and a weight of about 100,000 N. 1 N/m 2 is a Pascal atm x Pa psi

29 Pressure in a fluid is due to the weight P Force Area of a fluid. P mg ( V) g A A ( Ah) g A gh Pressure depends on Depth!

30 Measuring Pressure 5 1atm 1.013x10 Pa Why is the pressure at X equal to atmospheric pressure? P gh Because if it didn t, the mercury would be pushed out of the dish! P mercury gh h h P mercury g 2 101,300 N/ m 13, 600 kg / m x9.8 m / s 3 2 mercury water 13.6 water 1000 kg / m 3 h 760mm

31 Measuring Pressure Can a barometer be made with Water instead of Mercury? P h water P water gh g h 2 101,300 N/ m 1000 kg / m x9.8 m / s 3 2 mercury water 13.6 water 1000 kg / m 3 h 10.3m (Notice: 10.3m is just 13.6 x 760mm!)

32 Absolute vs. Gauge Pressure Absolute Pressure: P P gh 0 Guage Pressure: P0 gh Guage pressure is what you measure in your tires Absoulte pressure is the pressure at B and is what is used in PV = nrt

33 P V = nrt n = # moles R = 8.31 J/(mol-K) Universal Gas Constant Note: PV is units of Energy!

34 Atomic Units The Basics Atomic Number: # protons Atomic Mass: # atomic mass units (u) Atomic Mass Unit: 1/12 mass of C-12 atom amu = u = 1.66 x kg Atomic Mass of C = u (1% is C-13) Mass of 1 C = (12.011u) (1.66 x kg/u)

35 Moles and Avogadro s Number N A = x mol -1 Mole (mol) = # atoms or molecules (particles) as are in 12 grams of Carbon-12: 1 mole = x particles Avogadro s Number: the number of particles in one mole: N A = x mol -1 # moles n contained in a sample of N particles: n = N/ N A # particles in a sample is: N = n N A

36 More on Moles The mass / mol for any substance has the same numerical value as its atomic mass: mass/mol C-12 = 12 g / mol mass/mol Li = g / mol n = mass / (mass/mole) = mass / atomic mass n = mass / atomic mass

37 Q: How many moles are in 1 kg of Sodium? mass/mole = atomic mass Na: g / mol n = mass / (mass/mole) = 1000 g / ( g/mol) = 43.5 moles Q: How many atoms in 1 kg of Sodium? # particles in a sample is: N = n N A N = (43.5mol) x mol -1 = 2.62 x atoms

38 P V = nrt n = # moles R = 8.31 J/(mol-K) Universal Gas Constant PV = Nkt N= # particles k =1.38 x J/K Boltzmann s Constant Note: PV is units of Energy!

39 The only interaction between particles are elastic collisions (no sticky - no loss of KE) This requires LOW DENSITY Excellent Approximation for O, N, Ar, room temperature and pressures State is described by the Ideal Gas Law Non Ideal are Van der Waals gases

40 Ideal Gas Problem An ideal gas with a fixed number of molecules is maintained at a constant pressure. At 30.0 C, the volume of the gas is 1.50 m 3. What is the volume of the gas when the temperature is increased to 75.0 C? PV nrt 1 1 PV nrt 2 2 V V T 1 1 T 2 2 V T V T K 1.5m m 3 303K

41 Heat flows from HOT to COLD Conduction (solids) Convection (liquids & gases) Radiation (solids, gases, plasma)

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43 Energy transferred via molecular collisio

44 Heat energy is transferred in solids by collisions between free electrons Good Conductors: Most Metals (free electrons!) Bad Conductors: Organic & Inert Materials and vibrating atoms. Good Insulators: Air, Water, Wood Good Conductors are BAD Insulators

45 The heat Q conducted during a time t through a material with a thermal conductivity k. dt/dx is the Temperature Gradient. dt P ka dx

46 Some Thermal Conductivities

47 Temperature Gradient The quantity dt / dx is called the temperature gradient Q t ka dt dx dt T T h dx L c

48 Compound Slab: R values For a compound slab containing several materials of various thicknesses (L 1, L 2, ) and various thermal conductivities (k 1, k 2, ) the rate of energy transfer depends on the materials and the temperatures at the outer edges: i A Th T Li ki c Substances are rated by their R values R = L / k and the rate becomes A T h i T For multiple layers, the total R value is the sum of the R values of each layer Wind increases the energy loss by conduction in a home R i c

49 Conduction Problem T L T h c ka A bar of gold is in thermal contact with a bar of silver of the same length and area as shown. One end of the compound bar is maintained at 80.0 C while the opposite end is at 30.0 C. When the energy transfer reaches steady state, what is the temperature at the junction? Ignore thermal expansion of the metals.

50 In the same room, at the same temperature, the tile floor feels cooler than wood floor. How can they be the same temperature?

51 Hot Air rises, expands and cools, and then sinks back down causing convection currents that transport heat energy. Hot air rises because fast moving molecules tend to migrate toward regions of least obstruction - UP - into regions of lesser density! Rising air cools because a decrease in density reduces number of collisions & speeds decrease. As the air cools, it becomes denser, sinking down, producing a convection current.

52 Uneven heating on the earth and over water cause convection currents in the atmosphere, resulting in WINDS. Global wind patterns (Trade Winds, Jet Streams) are due to convection current from warmer regions (equator) to cooler regions (poles) plus rotation of Earth. Convection Currents in the Ocean (Gulf Stream) transport energy throughout the oceans. Air & Ocean Convection causes the WEATHER.

53 Convection between water and land causes the Winds.

54 Sea Breeze

55 High Pressure Dry Warm Weather Low Pressure Stormy Weather

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58 Electromagnetic Radiation is emitted and absorbed via atomic excitations. All objects absorb and emit EM waves.

59 Electromagnetic Radiation is emitted and absorbed via atomic excitations. All objects absorb and emit EM waves.

60 Frequency ~ Temperature When an object it heated it will glow first in the infrared, then the visible. Most solid materials break down before they emit UV and higher frequency EM waves. Long Short

61 Stefan s Law P = σaet 4 P is the rate of energy transfer, in Watts σ = x 10-8 W/m 2. K 4 A is the surface area of the object e is a constant called the emissivity e varies from 0 to 1 The emissivity is also equal to the absorptivity T is the temperature in Kelvins

62 A good absorber reflects little and appears Black A good absorber is also a good emitter.

63 P 4 e T A Radiant heat makes it impossible to stand close to a hot lava flow. Calculate the rate of heat loss by radiation from 1.00 m 2 of 1200C fresh lava into 30.0C surroundings, assuming lava s emissivity is 1. The net heat transfer by radiation is: P e A( T T ) P e A( T T ) (5.67 x10 J / smk )1 m (( K) ( K) ) P 266kW

64 How do fur coats keep you warm? Fur is filled with air. Convection currents are slow because the convection loops are so small.