Herriman High Honors Physics Chapter 9 Temperature and Heat

Herriman High Honors Physics Temperature Scales Temperature is defined as a measure of the average kinetic energy of the molecules. Temperature scales were developed using the freezing and boiling points of water at sea level as the standard reference points.

Herriman High Honors Physics Temperature Scales There are three Temperature Scales used in Science Fahrenheit – Used primarily in the United States Celsius – the standard for the Metric System Kelvin – Also know as the “Absolute Zero” Scale.

Herriman High Honors Physics Standard Reference Points ScaleBoiling PointFreezing Point Fahrenheit212 °F32 °F Centigrade100 °C0 °C Kelvin373273

Herriman High Honors Physics Conversion Equations Fahrenheit to Centigrade C = 5/9 (F – 32) Ex: C = 5/9 (212-32) = 100 Centigrade to Fahrenheit F = (9/5 C) + 32 Ex: F = (9/5)(100) + 32 = 212

Herriman High Honors Physics Conversion Equations Centigrade to Kelvin K = C +273 Ex: K = = 373 Kelvin to Centigrade C = K Ex: K = = 100 You Try Practice Set A P. 303 #1,3,& 5

Herriman High Honors Physics Heat Heat is a form of Energy Transfer Heat flows from areas of high energy to areas of lower energy Heat is transferred three way Conduction – requires contact Convection – mass movement of molecules Radiation – transfer over a distance

Heat Heat has the units of Energy English System – calories – the amount of energy required to raise the temperature of 1 gram of water 1°C. Metric System – Joule – 4.18 Joules in one calorie. Herriman High Honors Physics

Conservation of Energy ΔPE + ΔKE + ΔU = 0 The change in potential energy + the change in kinetic energy + the change in internal energy = 0 Energy is not created or destroyed, it just changes form. Herriman High Honors Physics Practice B P. 311 Problems 2 & 4

Herriman High Honors Physics Thermal Expansion Most objects tend to expand when their temperature rises and to contract when the temperature drops. Do you know what the one notable exception is?

Herriman High Honors Physics Thermal Expansion Objects can expand linearly whereas liquids expand volumetrically! Each substance has a constant for which describes its ability to expand. Linear constants are denoted by the Greek letter alpha, α and the volumetric constant is denoted by the Greek letter beta, β.

Herriman High Honors Physics Conduction Each material has an innate ability to absorb or give off heat – specific heat The amount of heat an object can transfer depends upon three things: The mass of the object, m, (in Kg) The specific heat of the object, C p, ( in J/g°C) The temperature change of the object, t, (in ºC)

Herriman High Honors Physics Calorimetry The symbol for heat is a capitol Q Law of Conservation of Energy says that Q lost = Q gained Mathematically Q = mC p Δt

Herriman High Honors Physics Sample Problem How much energy is required to raise the temperature of 5 Kg of water from 0°C to 100°C ? (C p = 4186 J/kg°C) Q= m C p Δt = (5 kg)(C p = 4186 J/kg°C)(100°C) = Joules

Herriman High Honors Physics Sample Problem A 5 Kg copper ball is heated to 180 ºC and dropped into a container of water at 100 °C. When the temperature of the ball/water system equalizes the final temperature is found to be 110 ºC. How much water is in the container? (C p = 390 J/Kg°C)

Herriman High Honors Physics Solution Q lost =Q gained Q copper = Q water mC copper Δt = mC water Δt (5 kg)(390 J/Kg°C)(70°C)=m(4186 J/Kg°C)(10°C) m = 3.26 kg Practice C p. 316 Problems 1 & 3

Herriman High Honors Physics Phases Changes Phase changes require that a substance absorb energy or release energy to occur. There is NO Change in Temperature associated with a phase change! Different words are used to denote direction when dealing with a phase change.

Herriman High Honors Physics Vocabulary of a Phase Change Freezing – change from liquid to solid. Energy is released! Melting – change from solid to liquid Energy is absorbed! Both of these changes happen at the same point; 0° for water!

Herriman High Honors Physics Vocabulary of a Phase Change Condensing – change from gas or vapor to a liquid. Energy is released! Boiling – change from liquid to gas or vapor Energy is absorbed! Vapor is the gas phase of any substance which is normally a liquid at room temperature!

Herriman High Honors Physics Energy Required for a Phase Change Just like specific heat is a set amount of energy for each substance – the amount of energy required for a phase change is also substance specific. Heat of Fusion – ΔH f, is the amount of energy absorbed or released when a substance melts or freezes!

Herriman High Honors Physics Energy Required for a Phase Change Heat of Vaporization – ΔH v, is the amount of energy absorbed or released when a substance boils or condenses! Mathematically: Q = mΔH f for Fusion or Q = mΔH v for Vaporization

Herriman High Honors Physics Sample Problem How much heat is required to melt 5 kg of ice at 0° C? Solution Q = mΔH f = (5 kg)(3.33 x 10 5 J/kg) = x 10 6 J

Herriman High Honors Physics Phase Diagram Ice Ice - Water Water Water- Steam Steam

Herriman High Honors Physics Sample Problem How much energy is required to convert 5 kg of ice at -5 °C to Steam at 120 °C? Steps Raise temperature of ice to melting point Melt Ice Raise temperature of Water to boiling point Vaporize Water Raise Temperature of Steam to 120 °C

Herriman High Honors Physics Solution Step 1: Raise temperature of Ice Q = mCΔt = (5 Kg)(2100 J/kg°C)(5 °C)= J Step 2: Melt Ice Q = mΔH f = (5 Kg)(3.33 x 10 5 J/kg) = J Step 3: Raise temperature of water to boiling Q = mCΔt = (5 Kg)(4186 J/kg°C)(100 °C)= J Step 4: Vaporize Water Q = mΔH v = (5 Kg)(22.6 x 10 5 J/kg) = J Step 5: Raise temperature of Steam to 120°C Q = mCΔt = (5 Kg)(2010 J/kg°C)(20 °C)= J Step 6: Get Total Q total = = J

Herriman High Honors Physics Convection & Radiation Convection – transfer of energy by mass movement of molecules Most common form is Wind Radiation – transfer of energy through waves – most common form is light or electromagnetic waves Will discuss both in more detail in later chapters

Herriman High Honors Physics Problem Types Temperature Scales and Conversions Thermal Expansion Conduction Calorimetry Latent Heat Fusion Vaporization