Thermal Energy & Heat Chapter 2 Section 3 5. Reactions a. Students know reactant atoms and molecules interact to form products with different chemical properties. b. Students know the idea of atoms explains the conservation of matter: In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same. c. Students know chemical reactions usually liberate heat or absorb heat. d. Students know physical processes include freezing and boiling, in which a material changes form with no chemical reaction. Chapter 2 Section 3

Energy What are four types of Energy? What is the SI unit for Energy? Energy: The ability to do WORK or cause change Law of Conservation of Energy: Energy is transformed. Energy is never created of destroyed

Thermal Energy Thermal Energy: - TOTAL kinetic energy of all the particles - When you describe matter as hot or cold. - Flows from warmer to colder matter. Simply put, thermal energy is kinetic energy at the molecular level. Temperature: Measurement of average energy of the motion of these particles. (Fahrenheit, Celsius, Kelvin) @ Higher Temp = particles move faster @ Lower Temp = particles move slower

What is heat? What is cold? What direction does heat always flow?

Endothermic Change vs. Exothermic Change Endothermic Change: Energy is taken in, or absorbed from surrounding matter. Example: Ice Melting Exothermic Change: Energy is released Example: Fire releases energy in form of heat

Endo- or Exo-? Is heat given off? Exothermic or Is heat taken away? Endothermic Making Ice Cubes (Liquid to Solid) Baking Bread Cooking an Egg A Burning Candle Dew Forming on Grass (Gas to Liquid) Burning Fuel (Liquid to Gas) Condensation (Gas to Liquid) Melting Butter (Solid to Liquid)

Chemical Energy Chemical Energy: The energy stored in chemical bonds between atoms Stored in Food, Gasoline, Human Body. . . When a chemical change occurs (example), chemical bonds are broken and new bonds are formed. Every bond has a certain amount of energy. To break the bond requires energy -- in chemical language it is called endothermic. These broken bonds then join together to create new molecules, and in the process release heat -- chemists call this exothermic.

Electromagnetic Energy A form of energy that travels through space as waves. Most notably, the sun! Radio waves, infrared rays (heat lamps), microwave oven, cellphones, UV rays, X-rays, WiFI. . . Waves are everywhere!

Electrical Energy The energy of electrically charged particles moving from one place to another Electrolysis: A chemical change with electrical energy that produces new substances

Vocabulary Check!

Example

Questions From where does the energy to heat water for hot chocolate originally come? Make a flow chart that traces the path that energy takes when you heat water for hot chocolate. On your flow chart, identify the form that energy takes at each step along the path. Was any energy lost during the energy transformations that heated the water for hot chocolate?