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23 effects of heat

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23 effects of heat

  1. 1. EFFECTS OF HEAT
  2. 2. EFFECTS OF HEAT Thermal Expansion  Change in Temperature  Phase Change 
  3. 3. THERMAL EXPANSION 1st Effect of Heat
  4. 4. THERMAL EXPANSION Addition of heat to a body may cause it to expand and shrinks when heat is removed. The expansion of objects can be observed in solids, liquids and gases. It is affected by several other factors.
  5. 5. THERMAL EXPANSION: SOLID
  6. 6. SOLIDS: LINEAR EXPANSION Change in length of a solid due to a change in its temperature  Depends on three factors:   original length, Li  change in temperature, ΔT  type of material / coefficient of linear expansion, 
  7. 7. SOLIDS: LINEAR EXPANSION Operational Definition: ΔL =  Li ΔT where: ΔL = change in length ( Lf – Li ) Li = original/initial length ΔT = change in temperature ( Tf - Ti )  = coefficient of linear expansion Temperature should be in °C or K, never °F Unit of  : °C-1 or 1/°C read as “per degree”
  8. 8. COEFFICIENTS OF LINEAR EXPANSION Material Aluminum α 22.2 Material German silver α 18.4 Material Marble α 9.8 Brass 18.7 Glass, hard 5.9 Nickel 13 Bronze 18 Gold 14.2 Platinum 9 Cement 10 Granite 7.9 Silicon 3 Cobalt 12 Iron, cast 10.4 Silver 19.5 Concrete 12 Iron, pure 12 Steel 13 Copper 16.6 Lead 28 Tin 23.4 Diamond 1.18 Manganese 22 Titanium 8.6
  9. 9. APPLICATIONS OF LINEAR EXPANSION Operational Definition: ΔL =  Li ΔT where: ) ΔL = change in length ( Lf – Li ) Li = original/initial length ΔT = change in temperature ( Tf - Ti  = coefficient of linear expansion Note: temperatures should be in °C or K Unit of  : °C-1 or K-1
  10. 10. THERMAL EXPANSION: LIQUID You will do better if you keep me in a cool dry place. *Winks*
  11. 11. THERMAL EXPANSION: LIQUIDS Operational Definition: ΔV =  Vi ΔT where: ΔV = change in volume ( Vf – Vi ) Vi = original/initial volume ΔT = change in temperature ( Tf - Ti )  = coefficient of volume expansion Note: temperatures should be in °C or K Unit of  : °C-1 or K-1
  12. 12. COEFFICIENTS OF VOLUMETRIC EXPANSION Material Acetone β 1430 Material Glycerine β 500 Alcohol, ethyl 1090 Kerosene 1000 Alcohol, methyl 1180 Mercury 180 Ammonia 2450 Olive oil 700 Chloroform 1270 Petroleum 1000 Gasoline 1000 Water 2140
  13. 13. THERMAL EXPANSION: GASES Don’t inflate me too much… especially on a hot day. 
  14. 14. THERMAL EXPANSION: GAS Charles’s Law : (Recall Gas Laws, Chemistry) Vi / Vf = Ti/ Tf Volume is directly proportional to temperature. (at constant pressure and number of moles) where: temperature should be in Kelvin
  15. 15. COEFFICIENT OF EXPANSION OF SOME MATERIALS Material SOLIDS Aluminum Brass Copper Concrete Iron Ordinary Grass Steel Tungsten LIQUIDS Ethyl Alcohol Gasoline Glycerin Mercury Water GAS Air  (x 10-6/°C)  (x 10-6/°C) 24 19 17 12 12 8.5 12 4.3 75 56 36 35 35 1100 950 500 180 210 3400
  16. 16. WORD PROBLEMS: 1. 2. 3. Solid. A 1.0 m long aluminum rod is heated from 30.°C to 50.°C. (a) By how much will it expand? (b) What will its final length be? Liquid. 75.0mL of ethyl alcohol at 10.°C is heated to 47°C. What will its final volume be? Gas. 250.0mL of oxygen is collected at 27°C at a particular pressure. What volume will the gas have at 35°C if the pressure remains the same?
  17. 17. TEMPERATURE CHANGE 2nd Effect of Heat
  18. 18. Temperature Change When heat is added to a system, its temperature increases.  When heat is removed from a system, its temperature decreases.   Factors that affect this temperature change  the type of material, C  amount of material, m  amount of heat added or removed, ∆Q
  19. 19. Temperature Change  Specific Heat Capacity (c) -  refers to the quantity of heat needed to raise the temperature of one gram of a substance by 1 °C. Operational Definition ∆Q = mc∆T Where: ∆Q m c ∆T is the heat required or supplied mass of the substance specific heat capacity of the substance change in temperature
  20. 20. Specific Heat Capacity (J/kg·K) Material Gold C 129 Material C Material C Granite 790 Wood 1700 Mercury 139.5 Sand 835 Steam 2080 Tin 227 Carbon dioxide 839 Ice 2110 Silver 233 Glass 840 Gasoline 2220 Copper 385 Concrete 880 Plastic 2302.7 Iron 450 Aluminum 897 Ethyl alcohol 2440 Steel 466 Oxygen 918 Paraffin wax 2500 Diamond 509.1 Air 1012 Water 4181.3
  21. 21. REVIEW  What is heat?  Heat is the transfer of energy.  What are the different modes of heat transfer?  conduction, convection and radiation  Heat transfers from _______ to _______.  from an area of higher temperature
  22. 22. EXTENDING  What happens when two objects of different temperature are made into contact?  Heat will transfer from the hotter to colder object.  What happens to the hotter object?  It gets colder because it loses energy when heat transfers from it to the colder object.  What happens to the colder object?  It gets hotter because it gains energy when heat transfers from the hotter object to itself.
  23. 23. EXTENDING  Will the heat transfer continue forever or will it eventually stop? If it will stop, when?  Heat transfer will stop when they reach the same temperature. This temperature is called equilibrium temperature.  At what temperature will they have thermal equilibrium?  At a temperature between the initial temperatures (not necessarily the average though)
  24. 24. EXTENDING  What happens when two objects of same temperature are made into contact with each other?  No heat transfer will occur.
  25. 25. Thermal Equilibrium  When two objects of different temperature are made into contact, heat transfer will occur.  Heat transfer will continue until both have the same temperature. When this happens, the two objects are now in thermal equilibrium.  The final temperature at which heat transfer stops is called the equilibrium
  26. 26. PHASE CHANGE 3rd Effect of Heat
  27. 27. Phase Change  Latent Heat - Addition of heat does not always results to a change in temperature; this heat could instead be used in changing the phase of some materials. This heat, which cannot be measured by thermometers, is called hidden or latent heat.  There are two types of latent heat:  Latent heat of Fusion  Latent heat of Vaporization
  28. 28. Latent Heat of Fusion ( hf )   heat needed to change 1 gram of a solid substance into 1 gram of liquid w/o changing its temperature OPERATIONAL DEFINITION hf = Hf / m or Hf = m hf where: hf = latent heat of fusion of material m = mass of material Hf = heat needed to change the material from solid to liquid without changing temperature
  29. 29. Latent Heat of Vaporization ( hv ) heat needed to change 1 gram of a liquid substance into 1 gram of gas w/o changing its temperature  OPERATIONAL DEFINITION hv = Hv / m or Hv = m hv where: hv = latent heat of vaporization of material m = mass of material Hv = heat needed to change the material from liquid to gas without changing temperature 
  30. 30. Example: How much heat is required to change 100. g of ice at -20oC to 120oC of steam?

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