Energy

1. Chapter 16 Energy

2. Energy: Ability to do Work Potential Energy = Energy of position AKA STORED ENERGY Kinetic Energy = Energy of motion Radiant Energy = Electromagnetic Ex: Sunlight

3. (Not a complete list!) Types of Energy

4. Units of Energy SI system - unit of energy is the JOULE (J) 1 Joule = amount of energy required to lift a golf ball 1 meter

5. Other Energy Units: • calorie, Calorie, BTU’s • 1 calorie = 4.18 Joules • 1 Calorie = 1000 calories = 1 kilocalorie

6. Kinetic Energy KE = ½ x Mass x Velocity2 = ½ mV2 So KE depends on how heavy and how fast

7. Potential Energy stapler Rubberband Popper Anything can have PE = energy of position = stored energy Potential Energy can be converted to Kinetic Energy

8. Magnets The potential energy in the system of 2 magnets depends on their relativeposition

9. Electromagnetic Radiation Sunlight – Visible radiation Ultraviolet radiation Infrared radiation Gamma rays X-rays Microwaves Radiowaves Applet spectrum

10. Energy in Chemistry Chemical energy = energy stored in bonds Heat – form of energy that flows from warmer object to cooler object (Macroscopic)

11. Heat Energy Heat: energy associated with the motion of atoms & molecules in matter (Microscopic) Symbol for heat energy = Q or q

12. Heat Energy Heat depends on amount of substance present We measure heat changes

13. Temperature = measure of average kinetic energy of particles of substance Swimming Pool vs. Mug Temperature is NOT energy Temperature does NOT depend on amount of substance; energy does

14. Law of Conservation of Energy Energy is neither created nor destroyed in ordinary chemical or physical change Energy before = Energy after Energy can be converted from one form to another - potential to kinetic - radiant to electric - electric to heat - chemical to kinetic - chemical to electrical

15. All physical & chemical changes are accompanied by change in energy The chemistry of energy changes is known as Thermochemistry!

16. Energy Transfer Measure changes in heat amount of energy transferred from one substance to another You can measureenergy lost somewhere or the energy gained somewhere else Cannotmeasure absolute heat content of system

17. Energy of Universe is conserved Universe Environment System Energy Energy can move between the system and the environment Environment

18. Exothermic Change System releases heat to environment What happens to the temperature of the environment? EXO - energy leaves system (exits) What happens to the energy level of the system? What happens to temperature of system?

19. EXO - energy leaves system (exits) Environment System Energy Temperature of environment  Temperature of system 

20. Exothermic Change System has net energy loss! Environment has net energy gain! Energy lost = Energy gained

21. Endothermic Change System absorbs heat from environment What happens to temperature of environment? Endo - Energy enters system What happens to the energy level of the system? What happens to temperature of system?

22. Endo - Energy enters system (entrance) Environment System Energy Temperature of environment  Temperature of system 

23. Endothermic Change System has net energy gain! Environment has net energy loss! Energy lost = Energy gained

24. Heat Flow Heat flows from hotter object to cooler object Cold pack on leg: Heat flows from the leg to the cold pack! Leg cools down; cold pack warms up

25. Quantity of heat transferred Quantity (amount) of heat transferred depends on Temperature change Mass of substance Specific Heat of substance

26. Calculating Heat Transferred Q = mCT Simple system: • pure substance in a single phase • calculate heat gained or lost using: Q = amount of heat transferred m = mass of substance C = specific heat capacity of the substance. T = temperature change = Tfinal – Tinitial

27. Specific Heat Amount heat energy required to raise temp of 1 gram of substance by 1oC Symbol = c Specific heat = a physical constant Different for each pure substance

28. Calorimeter

29. Another example source

30. Calorimetry Changes in heat energy are measured by calorimetry “universe” is contained in styrofoam cup “enviroment” is water**** “system” is whatever we put in the water

31. Calorimetry Energy lost = Energy gained Difficult to monitor “system” Easy to monitor “environment” (water) Energy lost/gained by environment = Energy gained/lost by system

32. Calorimetry 10 grams of NaOH is dissolved in 100 g of water & the temperature of the water increases from 22C to 30C was dissolving process endothermic or exothermic how do you know? Exothermic – temperature of environment ↑

33. Dissolving What’s happening when NaOH dissolves? Add H2O molecules close together, not interacting molecules pulled apart & interacting with H2O

34. Calorimetry Calculate energy released by NaOH as it dissolved in water Energy lost by NaOH = Energy gained by water Easier to calculate from H2O perspective Q = mCT Q = energy (joules) M = mass (grams) C = specific heat capacity (Table B) T = temperature change = Tf - Ti

35. Calorimetry & Q = mCT temperature of water increased from 22C to 30C 30C -22C = 8C = T What mass to use? Well, temp change was for water, so want mass of water m = 100 g Same goes for specific heat capacity; calculate heat absorbed by water cH20 = 4.18J/g

36. Q = mCT Q = (100 g)(4.18 J/g)(8C) Q = 3344 Joules

37. Stability and Energy • If energy is high, stability is low • If energy is low, stability is high