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Thermochemistry: Energy, Heat, and Laws of Thermodynamics

Explore the world of thermochemistry, where energy and heat play crucial roles. Learn about energy classifications, measuring energy changes, the 1st Law of Thermodynamics, and the difference between energy and heat. Dive into topics like exothermic and endothermic reactions, Hess's Law, entropy, and the 2nd Law of Thermodynamics. Discover how these concepts shape our understanding of energy transformations and reactions.

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Thermochemistry: Energy, Heat, and Laws of Thermodynamics

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  1. Thermochemistry Chapter 10

  2. Energy Energy-ability to do work or produce heat Ex: Cars need energy to run. People need energy to live.

  3. Energy Classifications • Potential energy-energy due to position or composition • Kinetic energy-energy due to motion

  4. Measuring Energy Changes • calorie(c)-amount of energy required to raise the temperature of one gram of water by one Celsius degree. (Food you eat is measured in Kilocalories which is abbreviated C). • Joule (J)-the SI unit of energy • 1 c=4.184J

  5. 1st Law of Thermodynamics • The law of conservation of energy states that energy cannot be created or destroyed. Therefore, the total energy in a system is conserved.

  6. What’s the difference between energy and heat?

  7. Temperature-measures the molecular motions of the particles • Heat(Enthalpy)-the flow of energy due to temperature difference **You can have temperature without having heat

  8. Exothermic reactions-energy flows out of the system. • Endothermic reactions-energy flows into a system. • q or H represents heat

  9. Label as exo or endo • Your hand gets cold when you touch ice. • Ice cream melts. • Propane is burning in a propane torch. • Water drops on your skin evaporate after swimming.

  10. Answers • Exohand+icewater+heat (your hand feels cold because heat is leaving, your hand has less energy after it touches the ice) 2) endo Ice cream+heat melted ice cream (the melted ice cream has more energy so heat must have been added to the system)

  11. 3) exo- propane gas  heat (heat is released) 4) endo water+body heatevaporation (in order for something to evaporate heat has to be added)

  12. Hess’s Law Hess’s Law-the overall enthalpy change in a reaction is equal to the sum of enthalpy changes for the individual steps in the process

  13. Entropy • Entropy-a measure of the disorder or randomness • Abbreviated with ∆S If you take a deck of cards and drop them on the floor, that would have high entropy. If you buy a new deck, that would have low entropy.

  14. 2nd Law of Thermodynamics • The entropy of the universe is always increasing • Processes in nature are driven toward lowest enthalpy and highest entropy

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