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ENERGY CHANGES & REACTION RATES

ENERGY CHANGES & REACTION RATES. Section 1 : Energy & Reactions. Heat : energy transferred between objects due to a difference in temp . measured in joules (J) ( flows from warmer to cooler object). Heat?. law of conservation of energy :

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ENERGY CHANGES & REACTION RATES

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  1. ENERGY CHANGES & REACTION RATES Section 1: Energy & Reactions

  2. Heat: • energy transferredbetween objects due to a differencein temp. • measured in joules (J) • (flowsfromwarmertocoolerobject) Heat?

  3. law of conservation of energy: • In all chemical or physical processes, energy is neither created nor destroyed • (it must go somewhere) • Energy changes always involve • the system and the surroundings. • system: • the focus(reaction) • surroundings: • everything else around

  4. Types of Systems OPEN SYSTEM: can exchange both matter and energy with the surroundings (e.g. open reaction flask, rocket engine) CLOSED SYSTEM: can exchange only energy with the surroundings (matter remains fixed) e.g. a sealed reaction flask ISOLATED SYSTEM: can exchange neither energy nor matter with its surroundings (e.g. a thermos flask)

  5. Energy & Chemical Reactions • Exothermic: • system releases heattosurroundings • Endothermic: • system absorbs heatfromsurroundings • feels warmer • temp up • feels cooler • temp down

  6. PE Diagram • ENDOthermic • products • potential • energy • (in bonds) • reactants • reaction progress • energy absorbed • “feels” cooler

  7. PE Diagram • EXOthermic • reactants • potential • energy • (in bonds) • products • reaction progress • energy released • “feels” warmer

  8. Describe the direction of heat flow as water melts. • from ___________ • to ___________ • ENDOthermic • surroundings • water

  9. During freezing weather, farmers protect citrus crops by spraying them with water. • This is because... • as water cools, it releases a lot of heat(EXO–) to the oranges.

  10. Bond Breaking & Bond Forming • Breaking bonds requires energy. • (endothermic) • Making new bonds gives outenergy. • (exothermic)

  11. Endothermic reaction • The energy needed to break the bonds is more than the energy released when new bonds are made. • 2N + 6H +4O • energy • Bonds in reactants are stronger • Energy released by forming bonds • Energy needed to break bonds • NH4NO3(aq) • Energy absorbed • NH4NO3(s) + H2O (l) • “reaction path”

  12. Exothermic reaction • The energy needed to break the bonds is less than the energy released when new bonds are made. • Bonds in products are stronger • C + 4H + 4O • energy • Energy needed to break bonds • Energy released by forming bonds • CH4(g) + 2O2(g) • Energy released • CO2(g) + 2H2O(l) • “reaction path”

  13. Quick Quiz! • 1. The energy released when a piece of wood is burned has been stored in the wood as ___________. • sunlight energy • heat energy • calories • chemical potential energy

  14. Quick Quiz. • 2. Which of the following statements about heat is FALSE? • Heat is a measure of temperature. • Heat always flows from warmer objects to cooler objects. • Adding heat can increase the amount of energy of an object. • Heat flows because of a difference in temperature.

  15. Quick Quiz. • 3. Fill in the blanks: • In an endothermic process, the system ________ heat when heat is ________ its surroundings, so the surroundings _____________. • gains, absorbed from, cool down. • loses, released to, heat up. • gains, absorbed from, heat up. • loses, released to, cool down.

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