# Chapter 14 Heat and Temperature: Temperature Energy Transfer Using Heat.

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Chapter 14 Heat and Temperature: Temperature Energy Transfer Using Heat

TN Standards CLE 3202.2.3 – Examine the applications and effects of heat energy CLE.3202.2.6 – Investigate the Law of Conservation of Energy CLE.3202.TE.3 – Explain the relationship between the properties of a material and the use of the material in the application of a technology

Section 1 - Temperature Key Questions: 1] What does temperature have to do with energy? 2] What three temperature scales are commonly used? 3] What makes things feel hot or cold?

Temperature and Energy Kinetic theory of matter –Matter is made of small particles always moving –Higher temperature, more motion –Large particles move slower The temperature of a substance is proportional to the average kinetic energy of the substance’s particles All particles have kinetic energy ( atomic )

Measuring Temperature As materials are heated, they expand Thermometers rely on expansion of liquids –Mercury or Alcohol Thermostats rely on expansion of metals

Temperature Scales Units: Fahrenheit ( English ) and Celsius ( metric ) Fahrenheit is English Celsius/Kelvin is metric Kelvin is an absolute scale –Absolute zero at -273.15 o C

Temperature Scales - Converting Celsius  Fahrenheit: T F = 1.8*T C + 32.0 Fahrenheit  Celsius: T C = ( T F – 32.0 ) / 1.8

Temperature Scales - Converting Celsius  Kelvin: T K = T C + 273.15 Kelvin  Celsius: T C = T K - 273.15

Temperature & Energy Transfer When you feel “hot” or “cold” you are detecting a temperature difference You are also feeling the affects of energy transfer Temperature changes indicate an energy transfer – temperature difference between two objects is felt as heat Heat is the energy transferred between objects of different temperature

Section 2 – Heat Transfer Key Questions: 1] How does energy transfer happen? 2] What do conductors and insulators do? 3] What makes something a good conductor of heat?

Energy Transfer ( Heat Flow ) What is happening in each picture Explain how heat is flowing ( ID how heat goes from one object to another ) What might be happening on the atomic level?

Different Methods of Transfer

Conduction occurs between objects in direct contact Thermal Conduction–heat source is one object

Different Methods of Transfer Convection results from the movement of warm fluids ( in contact with heat source ) Warm fluids rise –Cool when away from heat Cool fluids fall Convection current – Path of warm/cool fluids

Different Methods of Transfer Radiation does not require physical contact between objects Energy transferred as electromagnetic waves

Conductors & Insulators A conductor is a material through which energy can be easily transferred as heat An insulator is a material that transfers energy poorly Heat energy is transferred through particle collisions

Conductors & Insulators Heat energy is transferred through particle collisions Gases – poor conductors –Why? Denser materials usually are better conductors than less dense Metals – very good conductors Plastics – poor conductors

Specific Heat Determines how easily energy can be transferred as heat How much energy is needed to change the temperature of a substance by a certain amount

Specific Heat Amount of energy needed to raise the temperature of 1 kg of substance by 1 K Energy = specific heat x mass x temp change Energy = cmΔT

Specific Heat Temperature does not change when phases do; energy goes into phase change - not temperature adjustment Latent heat & Heat of Fusion –Gives amount of energy needed for phase change

Heat Flow Conceptual Practice Scenarios – Explain what is happening: 1] You pick up a coffee cup and it is hot 2] You touch a glass of cold SCHAWEET tea 3] A breeze makes you shiver

Heat Flow Conceptual Practice Which substance can you heat the quickest? One with a large or small heat capacity?

Heat Flow Math Practice How much energy must be transferred as heat to 200 kg of water ( c = 4,186 J/kg/K ) in a bathtub to raise its temperature from 25 o C to 37 o C?:

Section 3 – Using Heat Key Questions: 1] What happens to heat energy when it is transferred? 2] What do heat engines do?

Thermodynamics 1 st Law – total energy used in any process is conserved, whether that energy is transferred as work, heat, or both.

Thermodynamics 2 nd Law – energy transferred as heat ALWAYS moves from higher to lower temperature.

Thermodynamics Entropy – randomness or disorder of a system Thermo tells us that total entropy of the universe is ALWAYS increasing ( natural tendency )

Heat Engines

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