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Chemical Equilibrium Exergonic and Endergonic Reactions The Low of Mass Action, K eq and pK eq

Dr. M. Sasvári: Medical Chemistry Lectures 1. Chemical Equilibrium Exergonic and Endergonic Reactions The Low of Mass Action, K eq and pK eq Le Chatelier principle. A + B. AB. Reactants. Products. INI. I nitial state (initial concentrations) Standard conditions:

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Chemical Equilibrium Exergonic and Endergonic Reactions The Low of Mass Action, K eq and pK eq

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  1. Dr. M. Sasvári: Medical Chemistry Lectures 1. • Chemical Equilibrium • Exergonic and Endergonic Reactions • The Low of Mass Action, Keq and pKeq • Le Chatelier principle ChemEq 1

  2. A + B AB Reactants Products INI Initial state (initial concentrations) Standard conditions: 1 M of both the reactants and the products EQ Equilibrium state (eq. concentrations) Dynamic equilibrium Key terms and definitions Chemical reactions: forward reaction reverse reaction ChemEq 1

  3. A chemical reaction: INI EQ Exergonicreaction: Energy is released in the forward reaction - either exothermic or endothermic Endergonicreaction: Energy must beabsorbed for the forward reaction, otherwise reverse reaction happens ChemEq 1

  4. Examples Exergonic AND exothermic reactions Water formation H2(g) + 1/2O2(g)  H2O(g) -242 kJ ChemEq 1

  5. 2H+ 1/2O2 H2O in biological systems: Terminal oxidation production of heat and/or energy ChemEq 1

  6. Light production in an exergonic reaction Bioluminescence Light production in living organisms The American firefly produces light (phorphorescence) by the enzyme luciferase ChemEq 1

  7. Criminology: Luminol reagent with the iron in the hemoglobinwill glow with a blue light: Identification of bloodstains Light production in an exergonic reaction Chemoluminescence Production of light in a chemical reaction ChemEq 1

  8. water Exergonic ANDendothermic reactions Ba(OH)2 . (H2O)8 +2NH4Cl  Ba2+ + 2Cl- + 10 H2O + 2NH3 ChemEq 1

  9. sunshine 2H2O  4H + O2 Endergonic reactions (energy input is needed) ChemEq 1

  10. Definition of the equilibrium constant (Keq) ChemEq 1

  11. A + B AB INI 1 M 1 M 1 M EQ (1-x)M (1-x)M (1+x)M (1+x) Keq= (1-x) (1-x) [Products] Keq= [Reactants] If Keq > 1 Exergonic Reaction If Keq< 1 Endergonic Reaction ChemEq 1

  12. reactants products products reactants Keq > 1 Exergonic reactions Keq < 1 Endergonic reactions EQ: less products than reactants EQ: more products than reactants ChemEq 1

  13. The Low of Mass Action Cato Guldberg and Peter Waage 1867 ChemEq 1

  14. INI A + B AB forward reaction: vf = kf[A][B] where vf is the rate, kfis the rate constant of forward reaction reverse reaction: vr= kr[AB] where vris the rate, kris the rate constant of reverse reaction EQ Rate of the forward reaction = the rate of the reverse reaction ChemEq 1

  15. [AB] kf Ks = = kr [A][B] aA + bB cC + dD [C]c [D]d Ks = [A]a [B]b vf=vr kf[A][B] = kr [AB] For a general reaction: ChemEq 1

  16. Ks (Equilibrium constant for reactions in solution) A characteristic value for chemical reactions • Depends on - • - the temperature • - the pressure (gas) • Does not depend on - • - the concentrations • - the reaction rate/activation energy ChemEq 1

  17. pKs= -log Ks Endergonicreaction Exergonicreaction: Ks1 pKs0 > Ks1 pKs0 < > < Ks and pKs • More products • than reactants in EQ. • Less products • than reactants in EQ. ChemEq 1

  18. The range of Ks and pKs Ks 1010 100 1 0.01 10-10 pKs -10 -2 0 2 10 endergonic exergonic EQ ChemEq 1

  19. conc. of products Q = conc. of reactants conc. of products Ks= conc. of reactants Predicting the direction of a reaction Reaction quotient: INI (Initialconcentrations) Equilibrium constant: EQ (Equilibriumconcentrations) if Q < Keq : reaction will happen if Q = Keq : EQ if Q > Keq : reaction will happen forward reverse ChemEq 1

  20. Difference between Ks and Q shows the directionof the reaction ChemEq 1

  21. Dr. M. Sasvári: Medical Chemistry Lectures Le Chatelierprinciple (1884) Henri LeChâtelier (1850-1936) A French chemical engineer ChemEq 1

  22. The system is in EQ Start from EQ ChemEq 1

  23. INI EQ There is an effect on the system to remove it from EQ ChemEq 1

  24. The effect will be compensated INI ? New EQ Ksremains the same ChemEq 1

  25. A B INI new EQ more reactants are added The system will compensate the effect A B reaction goes forward or: productsare removed Effect of changing the concentrations A B EQ ChemEq 1

  26. Pressure is increased INI Compenzation: Reaction goes forwards to decrease the pressure new EQ Effect of changing the pressure (gaseous reactions) N2 + 3H2 2NH3 4 vol 2 vol volume decreases in the forward reaction EQ ChemEq 1

  27. A B Temperature is increased INI Reaction goes forwards to decrease the temperature new EQ Effect of changing the temperature endothermic reaction (heat is absorbed during forward reaction) EQ ChemEq 1

  28. [CoCl4]2-+6H2O [Co(H2O)6]2+ + 4Cl- blue pink Example Endothermic reaction OoC: turns to pink 20 oC: blue ChemEq 1

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