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Thermodynamics

Thermodynamics. Chemical reactions proceed according to the rules of thermodynamics The law of conservation of energy – energy can be converted from one form to another but the total amount of energy is constant Entropy – the universe is becoming more chaotic. ACK!. Thermodynamics.

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Thermodynamics

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  1. Thermodynamics • Chemical reactions proceed according to the rules of thermodynamics • The law of conservation of energy – energy can be converted from one form to another but the total amount of energy is constant • Entropy – the universe is becoming more chaotic ACK!

  2. Thermodynamics • Some constants • Gas constant: R = 8.315 Joules/K* mol or • 1.9872 cal/K.mol • Faradays constant: F = 96485 Joules/Volt.mol or • 23062 cal/Volt* mol

  3. Energy: definitions • Energy – ability to do work • Energetics – energy transfer • Types of energy • Potential– trapped energy • Kinetic – energy of movement

  4. Energy Categories: more definitions • Radiant energy – energy released from one object to another • Mechanical energy – energy to move objects from place to place • Electrical energy – energy that results from the movement of charged particles down a charge gradient • Thermal energy – reflected in the movement of particles and serves to increase temperature • Chemical energy – energy that is held within chemical bonds

  5. Energy Categories, Cont. • Animals rely on all five types of energy, which are interconvertible

  6. Food Webs are Transfers of Energy Figure 2.3

  7. Thermodynamics in a biological setting • Free Energy (G) • 1. Change in free Energy (ΔG) • ΔG = Products – Reactants • ΔG negative – reaction will proceed forward → • ΔG positive – reaction will proceed backward ← • ΔG zero – reaction at equilibrium ↔ • 2. Standard free Energy – ΔGo: 298 K (25oC), 1 atm pressure, pH 7.0 and 1M [initial] for all reactants and products

  8. Thermal Energy •  Thermal energy   movement of molecules • Most chemical reactions involve changes in thermal energy • Exothermic reactions – release heat • Endothermic reactions – absorb heat

  9. Chemical Reactions and Thermal Energy • Enthalpy • Enthalpy – average thermal energy of a collection of molecules i.e. bond energy • Change in enthalpy(DH) = Hproducts – Hsubstrates • Exothermic: DH is negative i.e. C6H12O6 + 6O2 → 6CO2 + 6H2O + energy • Endothermic: DH is positive i.e. ADP + Pi → ATP

  10. Chemical Reactions and Thermal Energy • Enthalpy and Entropy together • Entropy (S) – measure of randomness or disorder • Exothermic: DH is negative, increase in DS → reaction will occur spontaneously – negative DG • Endothermic: DH is positive, DS is positive → reaction will occur spontaneously. It has to overcome the positive DH

  11. Free Energy: calculations • Free energy changes of reactions are additive (coupled reactions): • Consider the phosphorylation of glucose to glucose 6-phosphate: • DGo: glucose + Pi ↔ glucose-6-phosphate + H2O = 3.3 kcal/mol • DGo: ATP + H2O ↔ ADP + Pi = -7.3 kcal/mol • Summing these reactions together:ATP + glucose ↔ ADP + glucose 6-phosphate   • DG° = +3.3 + (-7.3) = - 4kcal/mol (favourable)

  12. Biological reactions • DG = DGo + RTln ([products]/[reactants]) • Where R = gas constant, T = temperature in Kelvin • Example: • glucose + ATP ↔ glucose-6-phosphte + ADP • DGo: glucose + Pi ↔ glucose-6-phosphate + H2O = 3.3 kcal/mol • DGo: ATP + H2O ↔ ADP + Pi = -7.3 kcal/mol • Glucose: [5mM]; ATP: [2mM]; ADP: [0.15mM]; glucose-6-phosphate: [0.05mM] • So, DG = - 4.0 kcal/mol + 1.9872cal/K mol)(298K)ln((0.05*0.15)/(5*2)) • = -8.26kcal/mol

  13. ΔG for reactions that don’t make or break bonds • DGo is zero • - Examples: glucose transport, ion transport across membranes • DG = RTln ([inside]/[outside]) • Or for charged ions: • DG = RTln ([inside]/[outside]) + zFEm • where z = valence of the ion; F = Faraday constant and Em = membrane potential

  14. Transport across membranes • DG = RTln ([inside]/[outside]) + zFEm • where z = valence of the ion; F = Faraday constant and Em = membrane potential • Example: Diffusion of Cl- from out to in • Cl- outside cell: 120mM; Cl- inside cell: 10mM; Em = -80mV • DG = (1.987cal/K mol)(298K)(ln(10/120) + (-1)(23062 cal/V mol)(-0.08V) = • 376 cal/mol

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