A%20Simple%20Thought%20Experiment

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A Simple Thought Experiment
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Driving Forces for Natural Processes

• Enthalpy
• Tendency toward lowest energy state
• Form stablest bonds
• Entropy
• Tendency to maximize randomness

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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

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Entropy and Randomness
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Entropy and Randomness

• Entropy S measure of randomness
• cal/degmole
• T?S change of randomness
• For increased randomness, sign is

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System Definition
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System Definition
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System Definition
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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)

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1st Law of Thermodynamics

• Energy is conserved, but transduction is allowed
• Transduction

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2nd Law of Thermodynamics

• In all spontaneous processes, total entropy of
  the universe increases

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2nd Law of Thermodynamics

• ?Ssystem ?Ssurroundings ?Suniverse gt 0
• A cell (system) can decrease in entropy only if a
  greater increase in entropy occurs in
  surroundings
• C6H12O6 6O2 ? 6CO2 6H2O
• complex simple

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Entropy A More Rigorous Definition

• From statistical mechanics
• S k lnW
• k Boltzmann constant 1.38?1023 J/K
• W number of ways to arrange the system
• S 0 at absolute zero (-273ºC)

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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