Student Learning Objectives Heat & Temperature Chapter 5 Student Learning Objectives Relate kinetic energy to temperature Compare temperature scales Analyze systems to determine methods & effects of heat transfer

What does temperature measure? Temperature is a measure of the average kinetic energy of the atoms and molecules in a substance. We perceive the KE of atoms and molecules as being hot or cold. Harvards Golf Ball Atmosphere There is No Such Thing as Cold.

Materials at different temperatures reach thermal equilibrium when placed in contact.   Examples Thermometer + Person Person + Metal Chair Most materials expand when the temperature is increased, thermal expansion   Examples Metal lids Bridge Joints Bimetallic strips Hot Air Balloons https://www.youtube.com/watch?v=hX2Y2IDjuGI&feature=fvw https://www.youtube.com/watch?v=ZgTTUuJZAFs

Bimetallic Strip and Thermal Expansion Brass expands more than iron. The degree of deflection is proportional to the temperature. A/C thermostat and dial-type thermometers are based on bimetal coils. Invisible Motion Section 5.1

Liquid-in-glass Thermometer Thermometers are calibrated to two reference points (ice point & steam point.) Ice point – the temperature of a mixture of pure ice and water at normal atmospheric pressure Steam point – the temperature at which pure water boils at normal atmospheric pressure Usually contains either mercury or red (colored) alcohol Section 5.1

Temperature Scales Celsius, Kelvin, Fahrenheit Section 5.1

Temperature Scales Celsius, Kelvin, Fahrenheit Absolute Zero Ice Point Steam Point Diff. (Boil – Ice) Fahrenheit - 460o 32o 212o 180 Celsius -273o 0o 100o 100 Kelvin 273o 373o Section 5.1

Temperature Kelvin is based the average KE of atoms in a gas. Fahrenheit is based on boiling and freezing points of water.   320  freezing at sea level 212o  boiling at sea level Celsius is based on boiling and freezing points of water. 0 o  freezing at sea level 100o  boiling at sea level Kelvin is based the average KE of atoms in a gas.

F = (9/5)C + 32 C = (5/9)(F – 32) K = C + 273 0 Kelvin = ─273o C = ─460o F Object Kelvin Fahrenheit Human Body 310.15 K 98.6 ºF Sun 5800 K 9,980 ºF Blue Star 35000 K 62,540 ºF

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What is heat? Heat is energy that moves from one object to another if there is a temperature difference. The larger the temperature difference, the faster heat energy flows. These Practice Problems are presented in class Hot → Cold

Heat Unit SI - Calorie Since heat is energy, it has a unit of joules. (J) A more common unit to measure heat is the calorie. Calorie - the amount of heat necessary to raise one gram of pure water by one Celsius degree at normal atmospheric pressure 1 cal = 4.186 J (or about 4.2 J) Kilocalorie – heat necessary to raise 1kg water by 1oC 1 food Calorie = 1000 calories (1 kcal) 1 food Calorie = 4186 J (or about 4.2 kJ) Section 5.2

Expansion/Contraction with Changes in Temperature In general, most matter, solids, liquids, and gases will expand with an increase in temperature (and contract with a decrease in temperature.) Water is an exception to this rule – (ice floats!) Section 5.2

Thermal-Expansion Joints in a Bridge These joints allow for the contraction and expansion of the steel girders during the winter and summer seasons. Section 5.2

Behavior of Water  Strange! The volume of a quantity of water decreases with decreasing temperature but only down to 4oC. Below this temperature, the volume increases slightly. With a minimum volume at 4oC, the density of water is maximum at this temperature and decreases at lower temperatures. Most dense point Section 5.2

Behavior of Water: Structure of Ice Solid water takes up more volume (Ebbing, Darrell D., General Chemistry, Sixth Edition. Copyright 1999 by Houghton Mifflin Company) An illustration of the open hexagonal (six-sided) molecular structure of ice. This hexagonal pattern is evident in snowflakes. Section 5.2

Lakes freeze from the top down – Yellowstone Lake Photo Source: Copyright © Bobby H. Bammel. All rights reserved. Section 5.2

Specific Heat If equal quantities of heat are added to equal masses of two metals (iron and aluminum, for example) – would the temperature of each rise the same number of degrees? -- NO! Different substances have different properties. Specific Heat – the amount of heat necessary to raise the temperature of one kilogram of the substance 1oC Section 5.3

The amount of heat it takes to increase the temperature of a material by 1o C is the specific heat capacity of the material. c=specific heat capacity, m=mass, T=temperature (K or C) A substance with a high specific heat capacity will resist changes in temperature. See page 117 for different specific heat capacities Q = cmDT

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What is the greenhouse effect? What is global warming? The greenhouse effect traps heat near the surface of a planet. Greenhouse gasses in the atmosphere do not create heat. Greenhouse gasses slow heat loss to space. These Practice Problems are presented in class https://www.youtube.com/watch?v=ztWHqUFJRTs https://www.youtube.com/watch?v=lrEM3LHvjI0

What happens to temperature & energy during a phase change? A substance that has reached the temperature required for a phase change maintains its temperature during the phase change. All energy lost or gained is used to change the phase of the substance. Evaporation (Liquid to gas) Sublimation (Solid to gas) Condensation (Gas to liquid) https://www.youtube.com/watch?v=1MiQCBIx1mM

The amount of heat energy per kilogram that must be added or removed for a substance to change phase is called latent heat (L). IceWaterSteam Q = mL T (°C) 100 Joules

Graph of Temperature vs. Heat for Water Latent heat of fusion – heat necessary to go from A to B Latent heat of vaporization – heat necessary to go from C to D Section 5.3

Graph of Temperature vs. Heat for Water A=100% solid at 0oC B=100% liquid at 0oC C=100% liquid at 100oC D=100% gas at 100oC Section 5.3

Graph of Temperature vs. Heat for 1 kg of Pure Water 0.5kcal kg.Co 80 kcal 1.0 kcal/kg.Co 540 kcal 0.5 kcal/kg.Co Section 5.3

Other phase changes Sublimation – when a substance changes directly from solid to gas (dry ice  CO2 gas, mothballs, solid air fresheners) Deposition – when a substance changes directly from gas to solid (ice crystals that form on house windows in the winter) Section 5.3

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Heat Transfer Occurs by Conduction, Convection, and Radiation Section 5.4

What are the three methods of heat transfer? Conduction is the transfer of heat energy from one place to another by direct collisions. Solids tend to conduct heat better than liquids or gases. Why? Insulators slow or impede the rate of heat flow. Styrofoam Fiberglass Freely moving electrons = High thermal conductivity

Convection is the transfer of heat energy from one place to another by the bulk motion of groups of molecules in a fluid. (sinking/floating) Radiation is the transfer of heat energy from one place to another by electromagnetic waves (light).

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How are temperature and pressure related in a gas? In a gas, pressure is determined by temperature, volume, and number of particles. Boyle's Law: P1V1 = P2V2 Charles, Law: P1/T1 = P2/T2 PV = nkT

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What are the 3 laws of thermodynamics? 1st Law: The amount of heat energy transferred is equal to the change in internal energy plus work. Heat Energy  DIE + Work 2nd Law: Heat cannot flow spontaneously from a cold substance to a hot substance. Entropy (disorder) cannot spontaneously decrease. What is Entropy?

Laws of Thermodynamics Song 3rd Law: The entropy of a perfect crystal is zero when the temperature of the crystal is equal to absolute zero. KE → 0 Hero's Engine Laws of Thermodynamics Song Practice These Practice Problems are presented in class