Thermo#2

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Thermo#2

  1. 1. SYSTEM<br /> OPEN<br />ISOLATED<br /> CLOSED<br />Systems & Surroundings<br />In thermodynamics, the world is divided into a system and its surroundings<br />A system is the part of the world we want to study (e.g. a reaction mixture in a flask)<br />The surroundings consist of everything else outside the system<br />
  2. 2. OPEN SYSTEM: can exchange both matter and energy with the surroundings (e.g. open reaction flask, rocket engine)<br />CLOSED SYSTEM: can exchange only energy with the surroundings (matter remains fixed) e.g. a sealed reaction flask<br />ISOLATED SYSTEM: can exchange neither energy nor matter with its surroundings (e.g. a thermos flask)<br />
  3. 3. Exothermic<br />A chemical reaction or a physical change that releases heat <br />-energy flows out as a result of a temperature difference between the system and the surroundings<br />Exothermic processes have negative q<br /> reaction<br />
  4. 4. Endothermic<br />A chemical reaction or a physical change in which heat is absorbed - energy flows into a system from the surroundings.<br />Endothermic processes have positive q<br /> reaction<br />
  5. 5. Exothermic and Endothermic Processes<br />
  6. 6. Vaporization<br />Energy has to be supplied to a liquid to enable it to overcome forces that hold molecules together<br /><ul><li> endothermic process (q is positive)</li></ul>Melting<br />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<br /><ul><li> endothermic process (q is positive)</li></ul>Freezing<br />Liquid releases energy and allows molecules to settle into a lower energy state and form a solid<br /><ul><li> exothermic process (q is negative)</li></ul>(we remove heat from water when making ice in freezer) <br />

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