Heat Energy and Phase Changes Energy is the ability to do work. Measured in Joules.

Georgia Performance Standards SPS7. Students will relate transformations and flow of energy within a system. a. Identify energy transformations within a system (e.g. lighting of a match). b. Investigate molecular motion as it relates to thermal energy changes in terms of conduction, convection, and radiation. c. Determine the heat capacity of a substance using mass, specific heat, and temperature. d. Explain the flow of energy in phase changes through the use of a phase diagram.

Georgia Performance Standards SPS5. Students will compare and contrast the phases of matter as they relate to atomic and molecular motion. a. Compare and contrast the atomic/molecular motion of solids, liquids, gases and plasmas.

Temperature a measure of the average kinetic energy of the particles in an object As kinetic energy (motion) increases, temperature increases and vice versa A thermometer measures temperature Mercury Alcohol

Temperature Scales Celsius Scale (or Centigrade) ºC Freeze Water- 0 ºC Boil Water- 100 ºC Metric

Temperature Scales Kelvin Scale The lowest possible temperature is -273.16 ºC This is Absolute Zero- kinetic energy is zero, particles no longer move Kelvin, 0 K Absolute Zero is the basis of the Kelvin Scale Metric The magnitude of a degree Kelvin is the same as that of Celsius

Kelvin is the bigger scale. Temperature Scale Conversions K ºC K-273 ºC+273 From Celsius to Kelvin… add 273 From Kelvin to Celsius…subtract 273 Remember: #273 Kelvin is the bigger scale.

Math Skills Convert from Celsius to Kelvin 5 oC = __________ 110 oC =_________ 20 oC=___________ Convert from Kelvin to Celsius 350 K= __________ 280 K= __________ 125 K= __________

HEAT determined to be a form of energy BACKGROUND… people believed that heat was a colorless, odorless gas called Caloric… that would flow into objects and heat them up then flow out and cool down…NOT TRUE. Count Rumford- concluded that heat was a form of energy Motion can produce heat Amount of heat depends upon the amount of motion Heat is a form of energy caused by the internal motion of molecules of matter

Heat Unlike temperature, heat depends on mass Example: 50 g of water at 90 oC has more heat energy than 5g of water at 90 oC More heat energy = more severe burn

Energy Transfer Temperature changes indicate energy transfer Heat always moves from WARMER to COLDER Energy transfers when particles collide

Energy Transfer (1) Conduction- transfer of energy as heat through solid material Examples: ironing, touching hot pan… (2) Radiation- the energy that is transferred as electromagnetic waves Needs no air Example… microwave, fireplace, radiator..

Energy Transfer (3) Convection- heat transfer through liquids and gases… Examples.. Central air and heat, space heaters, blow dryer, convection currents (in water and air), boiling water, taking hot bath… While making smores you see tiny embers rising Convection Current- the vertical movement of air currents due to temperature variations Hot air rises taking the heat with it, Cool air replaces the air, the cool air is heated and then also rises, etc.

Back to #1 Conduction: Conductors and Insulators Conductor- transfers thermal energy easily Most Metals Insulator- DOES NOT transfer heat energy easily Attic insulation Plastic Rubber Wood Cotton Pure water

Specific Heat Specific Heat- Quantity of heat required to raise1 gram of material by one degree Celsius LOW SPECIFIC HEAT heats up quickly but loses heat as quickly (METALS have low specific heat) Mercury has very low specific heat… good for thermometers HIGH SPECIFIC HEAT heats up SLOWLY but retains heat longer (Water has high specific heat)

Heat lost or gained Formula Heat = mc∆T m= mass c= specific heat ∆ = change in T= temperature If I heat 110 grams of water from 25 degrees Celsius to 60 degrees Celsius, then I heat 120 grams of mercury from 20 degrees Celsius to 60 degrees Celsius. Which would heat up faster given the same heat source? How much heat is lost if I cool 85 grams iron from 180 degrees Celsius to 64 degrees Celsius? How much heat is gained if I heat 74 grams of silver from 110 degrees Celsius to 154 degrees Celsius?

Heat and Phase Changes Matter exists in 4 phases: solid, liquid, gas (and plasma) (plasma is high energy phase of matter found in stars and sun) A change in thermal energy causes a phase change Generally speaking… Least heat…SOLIDS  LIQUIDS  Gases … MOST heat

Phase changes Melting Freezing Vaporization (Boiling and Evaporation) Condensation Sublimation Freezing point- temp at which a liquid turns to solid Melting point- temperature at which solid turns to liquid Boiling point- temperature at which liquid phase turns to gas

Thermal Expansion Increase in size of substance caused by heat Most substances- Solid, Liquid, and Gas – Expand when heated Exception: Ice – expands when it cools from 4 oC to 0 oC, it

Math Skills The highest atmospheric temperature ever recorded on earth was 57.8 ºC. Express this temperature in degrees in Kelvins. How much heat is gained if I heat 92 grams of copper from 40 degrees Celsius to 98 degrees Celsius?