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Unformatted text preview: Some practice while you wait: Write out the rate law for the forward reaction. Write out the rate law for the reverse reaction. Don’t include pure liquids or solids. Coefficient becomes the exponent. Section 9.9 Catalysts AB + C → A + BC AB + C + X → A + BC + X E a > E aX so the reaction speeds up with the catalyst X Energy AB + C A + BC Reaction Coordinate without X with X E a E aX Enzymes are an example of catalysts. Allow reactions to occur in the body at low T. Section 9.10 Equilibrium Revisited Recall that as a reaction progresses,… ↓ [reactants] and ↑ [products] Eventually R f = R r & that’s equilibrium! ↓ R = k ( ↓ [reactants]) ↑ R = k ( ↑ [products]) Section 9.10 Equilibrium Revisited For the reaction at equilibrium: AB + C → A + BC k [AB][C] = k [A][BC] r = k f [products] k r [reactants] = = K Equilibrium Constant (K)  the concentration of the products divided by the concentration of the reactants at equilibrium. Section 9.10 Equilibrium Constant Ex. 2A ↔ A 2 The equilibrium constant can never be negative! (Concentrations can’t be negative.) For solutions , use molar concentration (mol/L) For gases , use the partial pressure in atm Solids and liquids are 1 so omit them from the equation General Form: aA +bB ↔ cC + dD K = [C] c [D] d [A] a [B] b A + B → AB K = [AB] [A][B] Section 9.10 Equilibrium Constant A very large K means an “extensive” reaction or the reaction goes to “completion”. (K >> 1) As much of the reactants are used as possible! Make as much as possible! Initial 5 mol 2 mol 0 mol Change2 mol2mol +2 mol Final 3 mol 0 mol 2 mol Reaction goes until B runs out “ limiting reagent ” Section 9.10 Equilibrium Constant A large K (but not huge) means the reaction goes until K is satisfied. (K > 1) Initial 6 mol 5 mol 0 mol Change4 mol4mol +4 mol Final 2 mol 1 mol 4 mol Reacts until correct ratio is reached!...
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 Spring '08
 BIGHAM
 Catalyst, Reaction, Solubility, Solvent

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