Chapter 10 Temperature and Heat I.Temperature A.Thermodynamics = study of heat and its effect on matter 1)One of the sub-fields of Physics 2)Part of Classical Physics (like Mechanics) developed by 1900 B.Measuring Temperature 1)What is hot? What is cold? 2)We must compare it to some other object 3)Use a thermometer to assign a temperature a)Sealed tube with a liquid inside (mercury or ethanol with a red dye) b)Volume of the liquid changes faster than the length of glass c)Volume increases until thermometer is same temperature as mouth d)101.6 o F is “hotter” than 98.6 o F e)Must have a scale of the thermometer to compare temperatures f)Could use other properties of matter than volume Length of a rod, electrical resistance, color change, etc…

4)Thermal Equilibrium = when touching objects no longer have changing properties 5)Zeroth Law of Thermodynamics = Objects in thermodynamic equilibrium have the same temperature B.Temperature Scales 1)Must have a standard scale to compare temperatures a)1 meter defined by a metal rod of a certain length b)Temperature standards use freezing point and boiling points of water 2)Fahrenheit ( ) a)Freezing point of water = 32 o F b)Boiling point of water = 212 o F c)Used primarily in USA 3)Celcius ( ) a)Freezing point of water = 0 o C b)Boiling point of water = 100 o C c)Used everywhere else and in science 4)1 o C > 1 o F 180 F o 100 C o

5)Conversion of Fahrenheit and Celcius Temperatures a)0 o C = 32 o F so there is a +/- 32 added into the conversion factors b)Convert 100 o C = ?? o F c)Convert 98.6 o F = ?? o C d)Prove to yourself that –40 o C = -40 o F D.Absolute Zero 1)0 o C is based on freezing point of water, could use ethanol (-115 o C) 2)Arbitrary point defined as zero, so we get negative numbers 3)What is the real lowest temperature = 0 ?

4)Pressure of a gas depends on its Temperature (constant volume) a)At the lowest possible temperature, P = 0 b)Lowest possible temperature = o C = Absolute Zero 5)Kelvin Temperature Scale: 0 K = absolute zero a)T K = T C b)Room Temperature = 22 o CT K = = K c)Not degrees Kelvin, but simply Kelvins d)Can’t ever reach absolute zero

II.Heat A.Zeroth Law = Objects in contact will come to the same temperature 1)Early explanation was the flow of “caloric” from hot to cold 2)Amount of caloric in an object = temperature 3)Also would work for mixture of liquids B.Heat = Q being transferred, not caloric, is responsible for equilibration 1)Heat is a form of Energy (unit = J) 2)Another unit is the calorie: 1 calorie = 4.19 J 3)1 calorie = amount of heat needed to raise the temperature of 1 g of water by 1 o C 4)Different materials require different amounts of heat to raise their temperature by the same amount 5)Specific Heat Capacity = c = amount of heat needed to raise the temperature of 1 g of a material by 1 o C (Units = cal/g o C) HotCold Hot object cools down Cool object heats up

6)Water has a very large heat capacity, so it cools things very well a)Small amount of water takes away a large amount of heat b)Temperature of the water is not raised very fast c)Coasts are cooler during the day, and warmer at night 7)Q = mc  T is used to relate mass, heat, heat capacity, and Temperature How much heat could 100 g of water and 100 g of steel take away if there temperatures were raised 50 o C? C.Heat and Temperature 1)Like caloric, Heat flows from Hot to Cold a)Added heat increases temperature b)Removed heat decreases temperature c)Temperature tells us direction of heat flow d)Temp depends on heat, mass, c

2)Heat = energy flowing between objects of different temperatures 3)Temperature = quantity that indicates direction of heat flow. If no heat is flowing, the objects are the same temperature. D.Heat and Change of Phase 1)Phases of matter depend on how much heat they have (temperature) a)Solid < Liquid < Gas b)Ice < Water < Steam 2)Block of ice at –20 o C a)Add heat: block warms up to 0 o C b)Add more heat: ice melts to water at 0 o C i.No temperature change ii.Change in phase requires heat 3)Latent Heat of Fusion = L f = amount of heat required to change the phase of 1 g of a solid to a liquid = 80 cal/g for water 4)Latent Heat of Vaporization = L v = amount of heat required to change the phase of 1 g of a liquid to gas = 540 cal/g for water How much heat is required to turn 15 g of liquid water at 100 o C to steam at 100 o C?

5)Ice added to water a)Ice is 0 o C b)Heat flows from water to ice i.Heats the ice to 0 o C ii.Then it starts melting the ice c)If there is enough ice, eventually all of the water will be cooled to 0 o C d)Both the ice and water will be at 0 o C = Thermal Equilibrium e)Heat from the surroundings eventually melts the ice f)After all ice melted, then the temperature will rise > 0 o C 6)Boiling Water = 100 o C 1)Add more heat, change some of it into steam 2)No change in temperature, all the heat goes to L v 3)High altitude lowers pressure needed to boil, less heat, b.p. = 96 o C at an altitude of 1 mile (Denver) 7)Q needed for 200 g ice (c = 0.5 cal/g o C) at –10 o C to melt? 17,000 cal