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THERMO-CHEMISTRY

Thermochemistry is the study of the heat changes that occur during chemical reactions. It involves understanding concepts such as energy, heat, enthalpy, temperature, and specific heat. This text provides an overview of these concepts and explains how to calculate heat changes in various scenarios.

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THERMO-CHEMISTRY

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  1. THERMO-CHEMISTRY

  2. Thermochemistry Study of the heat changes that occur during a chemical reaction

  3. Energy The capacity to do work or generate heat

  4. In chemistry, energy is stored in chemical bonds

  5. When bonds are made, energy is released. When bonds are broken, energy is absorbed.

  6. The main form of energy in chemistry is HEAT!

  7. Heat (q) Energy that is transferred between objects that have a temperature difference

  8. Heat always moves from a higher temp to a lower temp

  9. Terms to know: universesystemsurroundings

  10. Law of Conservation of Energy In any process, energy is neither created nor destroyed

  11. Some reactions absorb energy (heat) and some give off energy(heat).

  12. Exothermic Reaction A reaction that releases heat into the surroundings (heat exits)

  13. Endothermic Reaction A reaction that absorbs heat from the surroundings (heat goes en)

  14. Enthalpy Change (DH) Amount of heat lost or gained in a reaction (unit = kJ)

  15. Temperature (T) A measure of the average kinetic energy of the particles in a substance

  16. Heat (Q) Energy that is transferred between objects that have a temperature difference

  17. Heat (Q) Is measured in Joules (J) (or kJ) 1 kJ = 1000 J

  18. So…how do we measure heat? We can only measure changes in heat (absolute heat doesn’t exist)

  19. Specific Heat Amount of heat needed to raise the temp of 1g of a substance 1°C Unit =

  20. The Heat Equation Q = mCpDT Q = heat (joules-J) m = mass (grams) Cp = specific heat (J/g °C) DT = change in temp (°C)

  21. How much heat is needed to raise the temperature of 350 grams of water from 0.0°C to 25°C? 37000 Joules

  22. A 450 gram sample of water cools from 55°C to 10.0°C. How much heat is lost? 85000 Joules

  23. A 15.8-gram piece of zinc increases in temperature from 5.5°C to 6.9°C when 8.5 Joules of heat are added. What is the specific heat of zinc? 0.38 J/g°C

  24. calorie (cal) Quantity of heat needed to raise the temp of 1g of pure water 1°C

  25. How much heat is needed to increase the temperature of 10g H2O from 35°C to 45°C? 100 cal

  26. 1000 calories = 1 Calorie(Calorie is the kind on food labels, etc)

  27. 1 calorie = 4.184 Joules

  28. Calorimeter An insulated chamber used to measure the amount of heat absorbed or released during a reaction

  29. What happens when the phase is not changing: When heat energy is added, the molecules move faster and faster, increasing the temperature

  30. What happens during a phase change: When heat energy is added, instead of increasing the temperature (increasing the kinetic energy of the molecules), the intermolecular bonds are broken, changing the phase of the substance.

  31. PHASES OF WATER

  32. Heat of Fusion (Hf) Amount of heat necessary to convert a given amount of a solid into a liquid Q = mHf

  33. Heat of Vaporization (Hv) Amount of heat necessary to vaporize a given amount of liquid at its boiling point Q = mHv

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