Presentation on theme: "Heat, Temperature, Heat Transfer & Thermodynamics"— Presentation transcript:
1 Heat, Temperature, Heat Transfer & Thermodynamics
2 Heat vs. Temperature Heat Temperature A form of energy Measured in calories or JoulesThere is no “coldness” energyAny object with temperature above zero Kelvin has heat energyTemperatureAvg. Kinetic Energy of the particlesMeasured in C, F, K, R“hot” & “cold are relative termsAbsolute zero is zero Kelvin
3 Heat Transfer (3 methods) 1. Conduction - requires direct contact or particle to particle transfer of energy; usually occurs in solids2. Convection - heat moves in currents; only happens in fluid states of matter3. Radiation - heat waves travel through empty space, no matter needed; IR
4 Thermal EquilibriumA system is in thermal equilibrium when all of its parts are at the same temperature.Heat transfers only from high to low temperatures and only until thermal equilibrium is reached.
5 Temperature ScalesThere are four temperature scales – Celsius (Centigrade), Kelvin, Fahrenheit, & RankineCelsius, C – metric temp. scaleKelvin, K – metric absolute zero temp. scaleFahrenheit, F – customary (english) temp. scaleRankine, R – english absolute zero temp scale
6 Comparing Temperature Scales All temperatures listed are for waterCelsius - Freezing = 0°C, Boiling = 100°CKelvin - Freezing = 273K, Boiling = 373KFahrenheit- Freezing = 32°F, Boiling = 212°FConversions between Scales°F = 1.8 *°C+32 K = °C + 273
7 Change of StatesteamvaporizationHeat of fusion100condensationwaterTemp ° CmeltingHeat of vaporizationicefreezing-20Increasing Heat Energy (Joules)As heat is added to a substance it will either be absorbed to raise the temperature OR to change the state of matter.It can NEVER do both at the same time.Temperature will NOT change during a phase change!
8 Specific HeatThe amount of heat energy needed to raise the temperature of 1 gram of substance by 1°C.Substances with lower specific heats change temperature faster.Symbol : c units : cal/g°C or J/kg°CFor water: c = 1 cal/g°C = 4.18 J/g°C = 4180 J/kg°C
9 Latent HeatThe amount of heat energy required to change the state of 1 gram of substance.Heat of fusion - latent heat for changes between the solid and liquid phases. Lf =80 cal/g for waterHeat of vaporization - latent heat for changes between the liquid and gas phases. Lv =540 cal/g for water
10 Heat Calculations Q = mL Q = mcΔT Phase Change Temperature Change Q = heat absorbed or releasedm = mass of substance changing phaseL = latent heat of substanceLf = heat of fusion (liquid solid)Lv = heat of vaporization(liquid gas)Q = heat absorbed or releasedm = mass of substance being heatedc = specific heat of substanceΔT = change in temperature
11 Thermodynamics The study of changes in thermal properties of matter Follows Law of Conservation of Energy1st Law – the total increase in the thermal energy of a system is the sum of the work done on it and the heat added to it2nd Law – natural processes tend to increase the total entropy (disorder) of the universe.
12 1st Law of Thermodynamics The total increase in the thermal energy of a system is the sum of the work done on it and the heat added to it.ΔU = W + QΔU = change in the thermal energy of the systemW = work done on the system (W = Fd or W=ΔK)Q = heat added to the system(Q is + if absorbed, Q is – if released)*All measured in Joules*
13 Heat engines Convert thermal energy to mechanical energy Require high temp heat source and low temp heat sink. (Takes advantage of heat transfer process)Examples: Steam engine, Automobile engine
14 Refrigerators and Heat Pumps It is possible to remove heat from a cold environment and deposit it into a warmer environment.This requires an outside source of energy.Examples: Refrigerators, Air conditioning unitsHeat pumps are refrigeration units that work in either direction.
15 2nd Law of Thermodynamics All natural processes go in a direction that increases the total entropy of the universe.Entropy is a measure of the disorder of a system.If heat is added, entropy is increased.If heat is removed, entropy is decreased.Work with no ΔT, entropy is unchanged