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 moleculespossess.

Diagrams courtesy Doc Brown’s Chemistry Clinic website.

Dance of the Molecules…1. Fill 2 beakers with water; hot & cold2. Predict what will happen with drops of food coloring

added3. Add a drop or two of coloring and observe4. 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 CaCl2

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 JoulesTemperature-Measure of average kinetic energy per molecule; amount of hotness; Celsius, Fahrenheit or Kelvin scale

Temperature & HeatNo 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.

Heat Units: Joules. 4.2 Joules per 1g water 1 degree C =1 Calorie

1st 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.

2nd Law of Thermodynamics:Heat never spontaneously flows from a cold substance.

3rd Law of Thermodynamics:No system can reach absolute zero!

Specific Heat Capacity-Thermal Inertia

Low Specific Heat High Specific Heat

AluminumCalciumIronCarbonToast from ovenCrust of pieJoules/(g * K)

WaterIceSteamEthanolSoupCenter of pie fillingJoules/(g * K)

Thermal ExpansionMolecules 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 stripsExpansion joints on bridgesThermometer- Mercury

expandsEngineering –brass & iron

combinationPotholes on roadways-ice

expansionDentist- filling a cavity with

expansionFreezing a filled water bottle-