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Chemistry and Energy

How are they related?. Chemistry and Energy. Energy Encountered Daily. Is Heat Used or Released?. Endothermic reactions used heat from the surroundings Sweating Refrigeration Exothermic heat releases heat to the surroundings Hot hands Combustion Exercise. Endothermic Reactions.

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Chemistry and Energy

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  1. How are they related? Chemistry and Energy

  2. Energy Encountered Daily

  3. Is Heat Used or Released? • Endothermic reactions used heat from the surroundings • Sweating • Refrigeration • Exothermic heat releases heat to the surroundings • Hot hands • Combustion • Exercise

  4. Endothermic Reactions • Decrease in kinetic energy  decrease in temperature  heat will transfer from the environment to the system resulting in a cooler environment • Absorbs heat from its surrounding. • The system gains heat • Positive value for q • H = q = 0 • HproductsHreactants

  5. Exothermic Reactions • Increase in kinetic energy  increase in temperature of system heat released to the environment resulting in a hotter environment • Releases heat to its surroundings • The system loses heat • Negative value for q • H = q = 0 • HproductsHreactants

  6. Enthalpy • Heat content for systems at constant pressure • Symbol is H • Terms heat and enthalpy are used interchangeably for this course • H = q = m C T • Heat moves from ________ to ___________.

  7. Law of Conservation of Energy • Energy is not lost or gained in a chemical reaction •  In a chemical reaction potential energy is transferred to kinetic energy

  8. Thermochemical Equations • An equation that includes the heat change • Example: write the thermochemical equation for this reaction • CaO(s) + H2O(l) Ca(OH)2(s) H = -65.2 kJ CaO(s) + H2O(l) Ca(OH)2(s) + 65.2 kJ

  9. Stoichiometry and Thermochemistry Tin metal can be extracted from its oxide according to the following reaction: SnO2(s) + 4NO2(g) + 2H2O(l) + 192 kJ  Sn(s) + 4HNO3(aq) How much energy will be required to extract 59.5 grams of tin?

  10. How to solve • Use your stoichiometry • Treat heat as a reactant or product SnO2(s) + 4NO2(g) + 2H2O(l) + 192 kJ  Sn(s) + 4HNO3(aq) 59.5 g Sn 1 mol Sn 192 kJ 1 g Sn 1 mol Sn

  11. If an Object feels hot, it means it is undergoing a change with a H that is: a. positive b. negative c. whether the object feels hot or not is unrelated to its H d. I don’t know

  12. If the object feels hot, it means it is undergoing: a. an exothermic reaction b. an endothermic reaction c. whether it feels hot or not is unrelated to whether it is undergoing an exothermic or an endothermic change

  13. How does ice melt? Heat During a Change of State

  14. Molar Heat of Fusion • Heat absorbed by one mole of a substance during melting • Constant temperature • Hfus • H2O(s)  H2O(l) H = 6.01 kJ/mol

  15. Molar Heat of Solidification • Heat lost when 1 mole of a liquid solidifies • Temperature is constant • Hsolid • Hfus = -Hsolid • H2O(l)  H2O(s) H = -6.01 kJ/mol

  16. Molar Heat of Vaporization • Heat needed to vaporize 1 mole of a liquid • Hvap • H2O(l)  H2O(g) Hvap = 40.7 kJ/mol

  17. Molar Heat of Condensation • Heat released when 1 mole of vapor condenses • Hcond • H2O(g)  H2O(s) Hcond = -40.7 kJ/mol • Hvap = -Hcond

  18. Phase Change Diagram for Water

  19. Phase Change Diagram

  20. The House that Heats Itself • http://www.sciencefriday.com/videos/watch/10007

  21. CaLORIMETRY

  22. Calorimetry • Method used to determine the heat involved in a physical or chemical change. • Relies on the law of conservation of energy

  23. Calorimeter

  24. Simple Calorimeter

  25. Calorimetry Math • Heat gained by the water = q • Heat lost by the system = -q mCT = q T = Tf –Ti , m = mass, C = specific heat q gained by water = q lost by system • q water = - q system •  mCT = -mCT (mass H2O)(spec. heat H2O)(T H2O) = - (mass sys)(spec. heat sys)(T sys)

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