1 / 18

Chemical Equilibrium

Chemical Equilibrium. PHYS 1090 Unit 15. Direction. A chemical reaction proceeds in a specific direction under specific conditions. A  B. Why? Entropy increases!. Increase Entropy. Disperse matter Dissolve a solid in a liquid Melt a solid Release a gas Disperse energy

noah
Download Presentation

Chemical Equilibrium

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chemical Equilibrium PHYS 1090 Unit 15

  2. Direction • A chemical reaction proceeds in a specific direction under specific conditions. A  B • Why? Entropy increases!

  3. Increase Entropy • Disperse matter • Dissolve a solid in a liquid • Melt a solid • Release a gas • Disperse energy • Generate heat • Biggest effect at low temperature • When they conflict, one dominates. • Direction can change with temperature.

  4. Uncomplicated Examples • Dissolve CaCl2 in water • Gets hot: disperses energy • Solid dissolves: disperses matter • Burn wood: (C6H10O5)n(s) + 6n O2(g)  6nCO2(g) + 5nH2O(g) • Gets hot: disperses energy • Generates CO2 and H2O gas: disperses matter

  5. Complicated Examples • Dissolve NH4NO3 in water • Gets cold: constrains energy • Solid dissolves: disperses matter • Here, dispersing matter wins • Solidify super-cooled sodium acetate • Gets hot: disperses energy • Liquid solidifies: constrains matter • Here, dispersing energy wins

  6. Reaction Rates A  B • Rate is D[B]/Dt= –D[A]/Dt • Depends on • Intrinsic reactivity of A • Temperature • How much A there is • Proportional to [A]

  7. Reaction Rates A+ B  C • Rate is D[C]/Dt= –D[A]/Dt =–D[B]/Dt • Depends on • Intrinsic reactivity of A and B • Temperature • How much A and B there are • Proportional to [A][B]

  8. Rate constants A + B  C • Rate = k[A][B] • k = rate constant • Independent of [A], [B] • Depends on temperature

  9. Equilibrium  A  B • Two reactions: A  B and B  A • If both have the same rate, [A] and [B] don’t change • “Equilibrium” • kf[A] =kb[B] • [B]/[A] = kf /kb = K= equilibrium constant

  10. Equilibrium Constants • For A + B  C • For A + A  B • For A + B  C + D

  11. K = [HCl]2 K = [H2][Cl2] Examples NH3 + HCl  NH4Cl [NH4Cl] [NH3][HCl] H2 + Cl2 2 HCl

  12. Unchanging Concentrations • Solvent • Solid • Unmixed liquid Drop out of equilibrium constant

  13. [H2O][NaCl] K = [KOH][HCl] [NaCl] K = [KOH][HCl] Example KOH(aq) + HCl(aq)  H2O + NaCl(aq) • But H2O is the solvent: its concentration does not change. So:

  14. [H+][OH–] K = [H2O] Another Example H2O  H+(aq) + OH–(aq) • But again H2O is the solvent. So: K = [H+][OH–]

  15. [CaCO3][NaCl]2 K = [CaCl2][Na2CO3] [NaCl]2 K = [CaCl2][Na2CO3] Precipitation Example CaCl2(aq) + Na2CO3(aq)  CaCO3(s) + 2 NaCl (aq) • CaCO3 is a solid precipitate, not dissolved. So:

  16. Le Chatelier’s Principle • If a chemical system at equilibrium is perturbed, the system will adjust to minimize the perturbation

  17. Instances • If reactant concentration is high: • More product will be generated • If products are removed: • More product will be generated • If products are insoluble: • Effectively removes them • More product will be generated • (precipitation reactions)

  18. Instances • If a reaction generates a gas: • Increasing the pressure consumes products • Decreasing the pressure consumes reactants • Letting gas escape generates more • If a reaction generates heat: • Increasing the temperature inhibits it • Decreasing the temperature facilitates it

More Related