Some like it hot! Heat: Thermal Energy

What is Thermal Energy? What is the difference between a hot cup of coffee and a cold cup of coffee? The molecules in the hot cup of coffee are moving faster-they are more energetic! The warmer the object, the more kinetic energy its atoms and molecules possess. Diagrams courtesy Doc Brown’s Chemistry Clinic website.

Dance of the Molecules… 1. Fill 2 beakers with water; hot & cold 2. Predict what will happen with drops of food coloring added 3. Add a drop or two of coloring and observe 4. How do the observations support that hotter molecules move faster than molecules in cold objects? 5. Predict the activity in the beakers over the next few hours 6. Explain why a fragrant candle burning in a room gives off a scent to the other side. 7. Would the fragrance move more quickly or slowly in a cold room?

Chemistry Connections: Molar Enthalpy of Solutions- Movie 1. Give the equation for heat energy. 2. Define enthalpy. 3. What kind of energy is needed to separte the particles of a solid crystal? 4. Ammonium nitrate is a endothermic reaction. Why is this useful? 5. Why does the highway dept use CaCl 2 along with NaCl to reduce snow on roads?

Temperature- Celsius or Fahrenheit or Kelvin? Thermometers measure temperature by expansion or contraction of a liquid. Anders Celsius used the concept water freezes at 0°/boils at 100˚ Gabriel Fahrenheit made his freezing scale at 32˚/boiling at 212˚ Heat-Thermal energy that flows from high to low temperature; Calories or Joules Temperature-Measure of average kinetic energy per molecule; amount of hotness;Celsius, Fahrenheit or Kelvin scale

Temperature & Heat No outer limit on heat. Molecules can absorb more and more energy. Absolute zero- No motion in the atoms or molecules of a solid. NOVA: The Search for Absolute Zero- U-tube site. Matter contains thermal energy. Heat is thermal energy in transit. Cold is a lack of thermal energy.

1 st Law of Thermodynamics: Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred.

2 nd Law of Thermodynamics: Heat never spontaneously flows from a cold substance. 3 rd Law of Thermodynamics: No system can reach absolute zero!

Specific Heat Capacity-Thermal Inertia Low Specific HeatHigh Specific Heat Aluminum Calcium Iron Carbon Toast from oven Crust of pie Joules/(g * K) Water Ice Steam Ethanol Soup Center of pie filling Joules/(g * K)

Thermal Expansion Molecules warmed Increase in energy and movement- Molecules spread out as heat is added. Liquid water expands when warmed. When cooled between 4- 0 degrees– it expands setting up crystals: SNOW! Applications include: Thermostat –bimetallic strips Expansion joints on bridges Thermometer- Mercury expands Engineering –brass & iron combination Potholes on roadways-ice expansion Dentist- filling a cavity with expansion Freezing a filled water bottle-