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Thermo#2

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Transcript

  • 1. SYSTEM
    OPEN
    ISOLATED
    CLOSED
    Systems & Surroundings
    In thermodynamics, the world is divided into a system and its surroundings
    A system is the part of the world we want to study (e.g. a reaction mixture in a flask)
    The surroundings consist of everything else outside the system
  • 2. 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)
  • 3. Exothermic
    A chemical reaction or a physical change that releases heat
    -energy flows out as a result of a temperature difference between the system and the surroundings
    Exothermic processes have negative q
    reaction
  • 4. Endothermic
    A chemical reaction or a physical change in which heat is absorbed - energy flows into a system from the surroundings.
    Endothermic processes have positive q
    reaction
  • 5. Exothermic and Endothermic Processes
  • 6. Vaporisation
    Energy has to be supplied to a liquid to enable it to overcome forces that hold molecules together
    • endothermic process (q is positive)
    Melting
    Energy is supplied to a solid to enable it to vibrate more vigorously until molecules can move past each other and flow as a liquid
    • endothermic process (q is positive)
    Freezing
    Liquid releases energy and allows molecules to settle into a lower energy state and form a solid
    • exothermic process (q is negative)
    (we remove heat from water when making ice in freezer)

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