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A Simple Thought Experiment

A Simple Thought Experiment. Driving Forces for Natural Processes. Enthalpy Tendency toward lowest energy state Form stablest bonds Entropy Tendency to maximize randomness. Enthalpy and Bond Strength. Enthalpy = ∆H = heat change at constant pressure Units cal/mole or joule/mole

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A Simple Thought Experiment

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  1. A Simple Thought Experiment

  2. Driving Forces for Natural Processes • Enthalpy • Tendency toward lowest energy state • Form stablest bonds • Entropy • Tendency to maximize randomness

  3. Enthalpy and Bond Strength • Enthalpy = ∆H = heat change at constant pressure • Units • cal/mole or joule/mole • 1 cal = 4.18 joule • Sign • ∆H is negative for a reaction that liberates heat

  4. Entropy and Randomness

  5. Entropy and Randomness • Entropy = S = measure of randomness • cal/deg·mole • T∆S = change of randomness • For increased randomness, sign is “+”

  6. “System” Definition

  7. “System” Definition

  8. “System” Definition

  9. Cells and Organisms: Open Systems • Material exchange with surroundings • Fuels and nutrients in (glucose) • By-products out (CO2) • Energy exchange • Heat release (fermentation) • Light release (fireflies) • Light absorption (plants)

  10. 1st Law of Thermodynamics • Energy is conserved, but transduction is allowed • Transduction

  11. 2nd Law of Thermodynamics • In all spontaneous processes, total entropy of the universe increases

  12. 2nd Law of Thermodynamics • ∆Ssystem + ∆Ssurroundings = ∆Suniverse > 0 • A cell (system) can decrease in entropy only if a greater increase in entropy occurs in surroundings • C6H12O6 + 6O2  6CO2 + 6H2O complex simple

  13. Entropy: A More Rigorous Definition • From statistical mechanics: • S = k lnW • k = Boltzmann constant = 1.3810–23 J/K • W = number of ways to arrange the system • S = 0 at absolute zero (-273ºC)

  14. Gibbs Free Energy • Unifies 1st and 2nd laws • ∆G • Gibbs free energy • Useful work available in a process • ∆G = ∆H – T∆S • ∆H from 1st law • Kind and number of bonds • T∆S from 2nd law • Order of the system

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