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TOPIC: ENERGY

TOPIC: ENERGY. Do Now:. All physical & chemical changes are accompanied by change in energy. The chemistry of energy changes is known as Thermochemistry!. Stability and Energy. If energy is high, stability is low If energy is low, stability is high.

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TOPIC: ENERGY

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  1. TOPIC: ENERGY Do Now:

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

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

  4. Energy: Ability to do WorkThe SI unit for an energy measurement is called the Joule (J)EXAMPLE: 1 Joule = amount of energy required to lift a golf ball 1 meter

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

  6. (Not a complete list!)

  7. Kinetic Energy (KE) – energy of motion • KE = ½ x Mass x Velocity2 = ½ mV2 • KE depends on how heavy and how fast Kinetic Molecular Theory: the atoms and molecules making up substances are in constant motion

  8. Potential Energy (PE): energy of position; stored energy of matter • EXAMPLES • stapler • Rubberband

  9. When Potential energy is released from matter it becomes kinetic energy

  10. Energy in Chemistry=chemical energyheat energy

  11. Chemical Energy • energy stored in bonds; it is released as the result of a chemical reaction

  12. Heat Energy Heat: energy that is in the process of flowing from warmer object to a cooler object Symbol for heat energy = Q or q The amount of heat required to raise the temp. of 1 gram of water 10C = a calorie

  13. Other Energy Units: • calorie, Calorie, BTU’s • 1 calorie = 4.18 Joules • 1 Calorie = 1000 calories = 1 kilocalorie • NOTE: When your body breaks down food, these reactions give off heat – which is measured in calories (That’s why your food is labelled in calories)

  14. Environment System Energy energy (heat) is given off = exothermic EXO - energy leaves system (exits) Temperature of environment  Temperature of system 

  15. Environment System Energy energy (heat) is absorbed = endothermicEndo - Energy enters system (enter) Temperature of environment  Temperature of system 

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

  17. Calorimeter: an insulated devise used for measuring the amount of heat absorbed or released during a chemical or physical change

  18. “universe” is contained in Styrofoam cup “environment” is water**** “system” is whatever put in water Energy lost = Energy gained Difficult to monitor “system” Easy to monitor “environment” (water) Energy lost/gained by environment = Energy gained/lost by system

  19. The amount of heat transferred depends on 3 things Temperature change Mass of substance Specific Heat of substance

  20. Specific Heat Found in Table B • The amount of heat required to raise the temp of any given substance by 10C • Symbol = c • Specific heat = a physical constant • unique for each pure substance

  21. Calculating Heat Transferred Q = mCT Simple system: • pure substance in 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

  22. 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 ↑

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

  24. Calorimetry Calculate energy released by NaOH as it dissolves 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

  25. 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

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

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