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Energy

Energy. L. A tale of two types. Exothermic. Potential Energy. Kinetic Energy. Energy of motion Measurement of Temperature °C – relative K - actual. Endothermic. Stored energy Based on composition or location Measured with: Measured in: Calories (cal) Joules (J). L.

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Energy

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  1. Energy L

  2. A tale of two types Exothermic Potential Energy Kinetic Energy Energy of motion Measurement of Temperature °C – relative K - actual Endothermic • Stored energy • Based on composition or location • Measured with: • Measured in: • Calories (cal) • Joules (J) L

  3. The Law of Conservation of Energy • Energy can neither be created nor destroyed, it can only change forms • Energy is the ability to do work or produce heat

  4. Specific Heat (c) • The amount of energy to raise 1g of a substance by 1°C • Unique to a substance q = mcDT q = heat (J or cal) m = mass (g) c = specific heat (J/(g°C) –or-- cal/(g°C)) DT = change in temperature (°C)

  5. Specific Heat continued The temperature of a sample of iron with a mass of 10.0g changed from 50.4°C to 25.0°C with the release of 114 J heat. What is the specific heat of iron? q = mcDT 114 J = 10.0g (c) (50.4°C – 25.0°C) 114 J = 254 g°C (c) 0.449 j/g °C

  6. Practice • If the temperature of 34.4g of ethanol increases from 25.0°C to 78.8°C how much heat will be absorbed by ethanol? (cethanol = 2.44 j/g°C) • A 4.50g nugget of pure gold absorbed 276J of heat. What was the final temperature of the gold if the initial temperature was 25.0°C? (cgold = 0.129J/g°C) • 4520 J • 500 °C

  7. Vocabulary If this is a reaction “you are part of the system” • System – where the reaction is taking place and the elements involved • Surrounding – everything not the system

  8. Types of Reactions Endothermic Exothermic Releases energy System heat decreases Surrounding heat increases Bond formation is always exothermic Therefore energy is a product Conversion of PE to KE • Absorbs energy • System heat increases • Surrounding heat decreases • Bond breaking is always endothermic • Therefore energy is a reactant • Conversion of KE to PE

  9. In order for a reaction to proceed it must overcome the AE Heat of Products Heat of reaction Heat of Reactants

  10. Exothermic • ΔHreaction = Hproducts - Hreactants • H = heat (J) • ΔH is the change in the heat of the system under constant pressure. • Exothermic: –ΔH. • Makes kinetic energy • Endothermic: +ΔH. • Uses kinetic energy Endothermic • Potential Energy • Kinetic Energy

  11. What type of reaction is this: Endothermic DH is positive

  12. What type of Reaction is this:

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