Chapter_1_thermo_w09

Chapter_1_thermo_w09 - Chemistry 237 Thermodynamics and...

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Chemistry 237 Thermodynamics and Energy Transfers
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Energy Transfers in Metabolism Topics thermodynamics, briefly enthalpy entropy free energy equilibrium constants ΔG o ' coupled reactions “High Energy” compounds Phosphoesters
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system surroundings
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Enthalpy Enthalpy: The change in heat content of the system during a chemical reaction carried out at constant pressure. H > 0 reaction is endothermic, heat is absorbed. H < 0 reaction is exothermic, heat is given off. Review chapter 7 in the 9 th edition of Petrucci system surroundings
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Something to think about If a process in endothermic can it be energetically favorable “spontaneous”? Yes it can. Think about an ice cube in a room at 25°C.
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Chemists talking to their kids
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Entropy Second law of thermodynamics: “The universe tends toward maximum entropy.” S universe > 0 What is entropy? Disorder Energy dispersal
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Entropy S sys = q rev /T The change in entropy of the system is related to how the energy of the system is dispersed. Here is a qualitative picture q rev is the maximum amount of heat that can be transferred during a process. For chemical reactions it is the enthalpy change when the system is at equilibrium What is happening to the surroundings?
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Entropy The surroundings lose heat that is absorbed by the system. Compare entropy changes for system and surroundings What is happening to the surroundings?
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Spontaneity A chemical reaction is spontaneous if S universe > 0. S system + S surroundings = S universe S surroundings = - H system /T S universe = S system - H system /T
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G = H – TS A quantity that allows one to determine if a reaction is energetically favourable. For any process at constant P and T ΔG = ΔH - TΔS ΔG 0 standard free energy change for a reaction. When reactants and products are in their standard states Pure liquid or solid, solutions 1molL -1 and gases P =100kPa. Free Energy
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Free Energy • Free energy G is a state function. • It is path independent. • Hess’s Law applies to ΔG and ΔS as well as ΔH Given the ΔG for a reactions the ΔG of a combination can be calculated
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Food for Thought: i) relate the concept of entropy to the structure of water (we will address this question later in the next section) ii) if the universe tends to states of higher disorder, how do biological systems maintain the high degree of order necessary for Life?
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This note was uploaded on 07/07/2010 for the course BIOL 237 taught by Professor Daragilbert during the Fall '09 term at Waterloo.

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Chapter_1_thermo_w09 - Chemistry 237 Thermodynamics and...

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