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Penn State - CHEM 112 - Class Notes - Week 4

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Penn State - CHEM 112 - Class Notes - Week 4

School: Pennsylvania State University
Department: Chemistry
Course: General Chemistry
Professor: Raymond Shaak
Term: Spring 2016
Tags:
Name: Chem 112 - Week 4 Notes (Equilibrium)
Description: Notes from week 4 of Chem 112. Beginning concepts of chemical equilibrium.
Uploaded: 09/19/2016
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background image Chem 112                      9-14-16  Equilibrium    A state in which opposing forces or influence are balanced. (Google)   o  Chemistry-specific: A state in which a process and its reverse are occurring at equal  rates so that no overall change is taking place. (Google)    Equilibrium process example:   o  2NO + Br 2   2NOBr    Chemical Equilibrium   o  Preferred state of H 2 O at:     120 deg C: gas    Equilibrium reaction: H 2 O (l)  H 2 O(g)     37 deg C: liquid    Equilibrium reaction: H 2 O (l)  H 2 O (g)     -10 deg C: solid    Equilibrium reaction: H 2 O (s)  H 2 O (l)    100 deg C: gas    Equilibrium reaction: H 2 O (l)  H 2 O (g)    0 deg C: solid    Equilibrium reaction: H 2 O (s) H 2 O (l)   o  Note that, for different temperatures, the equilibrium reactions may be the same    They are further specified by K, the equilibrium constant  o  What state(s) of H 2 O are present at:     37 deg C: liquid 
  0 deg C: solid, liquid 
  100 deg C: liquid, gas 
  Key points about chemical equilibrium  o  At equilibrium, the relative concentration of reactants and products does not change  over time.   o  The ratio of the concentrations of products to reactants at equilibrium is the same  regardless of starting conditions.     Macroscopic vs. microscopic  o  Relative concentrations remain constant at equilibrium 
o  The reaction still occurs  
  The forwards and backwards expression of a same reaction will have equal rates, unequal to  zero    Equilibrium constant  o  Equilibrium constant (K eq ) defines the ratio of the amounts of products and reactants in  equilibrium reactions   o  K eq  is a constant; does not change when concentrations change    Concentrations change in order to match up with K eq  value 
background image   K eq  will change with temperature   o  K eq  expression for a reaction αA + ßB = γC + δD:     K eq  = [C] γ [D] δ /[A] α [B] ß   o  K eq  expression for CH 3 COOH (aq)  CH 3 COO - (aq) + H + (aq)    K eq  = [CH 3 COO - ][H + ]/[CH 3 COOH]   o  We can express amounts of chemical species as partial pressures or concentrations    K p   K eq  (partial pressures)     K c   K eq  (concentrations)     K p  = K c (RT) Δn     Δn = change in number of moles of gas    Heterogeneous equilibria  o  Homogeneous equilibria: all species are in the same phase 
o  Heterogeneous equilibria: species are in different phases 
o  How to write K
eq  expressions for heterogeneous equilibria:     CaCO 3  (s)  CaO (s) + CO 2  (g)     K eq  = K p  = PCO 2 ; K c  = [CO 2 ]    Pb 2+  (aq) + 2Cl -  (aq)  PbCl 2  (s)     K eq  = 1/[Pb 2+ ][Cl - ] 2     CH 3 COOH (aq)  H 3 O +  (g) + CH 3 COO -  (aq)     K eq  = [CH 3 COO - ][H 3 O + ]/[CH 3 COOH]  Chem 112                      9-16-16  Expressing K eq     Remember: pure liquids and solids will not appear in K eq  equations - Only aqueous and gaseous  molecules. Remember that K eq  is expressed as  products / reactants    Examples     CaCO 3  (s)  CaO (s) + CO 2  (g)   o  Autopilot first    K eq  = [CO 2 ][CaO]/[CaCO 3 o  Remove solids and liquids    K eq  = [CO 2 ] [CaO] / [CaCO 3 ]     K eq  = [CO2]    Pb 2+  (aq) + 2Cl -  (aq)  PbCl 2  (s)   o  Autopilot first    K eq  = [PbCl 2 ]/[Pb 2+ ][Cl - ] 2   o  Remove solids and liquids    K eq  =  [PbCl 2 ] /[Pb 2+ ][Cl - ] 2     K eq  = 1/[Pb 2+ ][Cl - ] 2     CH 3 COOH (aq) + H 2 O (l)  CH 3 COO -  (aq) + H 3 O +  (aq)  

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School: Pennsylvania State University
Department: Chemistry
Course: General Chemistry
Professor: Raymond Shaak
Term: Spring 2016
Tags:
Name: Chem 112 - Week 4 Notes (Equilibrium)
Description: Notes from week 4 of Chem 112. Beginning concepts of chemical equilibrium.
Uploaded: 09/19/2016
3 Pages 13 Views 10 Unlocks
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