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Thermochemistry

Thermochemistry. Chapter 10. Energy. Energy-ability to do work or produce heat Ex: Cars need energy to run. People need energy to live. Energy Classifications. Potential energy-energy due to position or composition Kinetic energy-energy due to motion. Measuring Energy Changes.

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Thermochemistry

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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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