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Thermochemistry

Chemistry Ms. Piela. Thermochemistry. Heat transfers in chemical reactions Energy Definition: The capacity to do work or supply heat Basic Types: Mechanical, Electrical, Potential, Kinetic. Thermochemistry –. Energy that is stored within chemical bonds

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Thermochemistry

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  1. Chemistry Ms. Piela Thermochemistry

  2. Heat transfers in chemical reactions • Energy • Definition: The capacity to do work or supply heat • Basic Types: Mechanical, Electrical, Potential, Kinetic Thermochemistry –

  3. Energy that is stored within chemical bonds • Determined by the arrangement and bonding of atoms • Examples: Gasoline, Food, etc Chemical Potential Energy

  4. Exothermic processes (‘exits’) • Heat flows out of a system Exothermic & Endothermic System Surroundings

  5. System loses heat (negative sign) Examples: Explosions!, Sun, Fire Exothermic and Endothermic

  6. Endothermic processes (‘enter’) • Heat is absorbed from surroundings Exothermic and Endothermic System Surroundings

  7. System gains heat (positive sign), Heat change is > 0 Examples: Boiling water, ice melting Exothermic and endothermic

  8. Energy transfers due to temperature differences between objects Flows from hot to cold until temperature equilibrium is reached Heat –

  9. Energy cannot be created or destroyed, only transferred • Can be transformed • Example: Law of Conservation of Energy –

  10. Calorie (cal) – the amount of heat needed to raise 1 gram of water 1 °C • Heat calorie is not to be confused with dietary calories • 1 dietary Calorie = 1 kcal = 1000 cal • Joule (J) – metric unit of heat and energy Units of Heat Conversion Factor! Woo! 1 cal = 4.184 J

  11. It takes 50.2 J to raise the temperature of a 100.0 g piece of glass. How many calories is this? Conversion Practice

  12. A small chocolate bar has about 210,000 calories. How many Joules is this? Conversation Practice

  13. The amount of heat required to raise 1 gram of a substance 1 °C Heat capacity is the amount of heat required to raise a substance 1 °C Specific Heat – VS.

  14. q = heat (J or cal) m = mass (g) C = specific heat ∆T = Change in Temp. (°C) Specific Heat Equation q = mC∆T

  15. Specific heat plays a role in buffering climates • Specific heat of land = 0.8 J/g ° C • Specific heat of water = 4.184 J/g °C • How does this help buffer climates? • Water heats up slower and cools down slowly, releasing heat gradually Specific Heat Application: Land vs. Water

  16. On the notes, you’ll see a table of specific heat capacities for common metals. We’ll be using these throughout all the problems in this section, so keep it handy! Table of Specific Heat Capacities

  17. A 1.55 g piece of stainless steel absorbs 141 J of heat when its temperature increases by 178 °C. What is the specific heat of stainless steel? Specific Heat Example 1 .511 J/g °C

  18. How much heat is required to raise the temperature of 250.0 g of mercury from 52 °C to 60 °C? Specific Heat Example 2 280 J

  19. If the initial temperature of a 10.0 g substance is 20.0 °C and 100.0 J of heat are absorbed, what is the final temperature? The specific heat of the substance is 1.15 J/g °C. Specific Heat Example 3 28.7 °C

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