CHEM 1C Lecture Notes - Dynamic Equilibrium, Reaction Rate Constant, Partial Pressure

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Published on 28 Aug 2013
School
UC-Irvine
Department
Chemistry
Course
CHEM 1C
Chem 1 C
Chap 14 Chemical Equilibrium
dynamic equilibrium
othe state of a reaction in which its forward and reverse reactions occur at equal
rates so that the concentration of the reactants and products does not change with
time.
chemical equilibrium
orate of forward and reverse reactions are equal and the concentrations of reactants
and products remain constant
physical equlibrium
oequilibrium between two phases of the same substance
o
ex. ice with water
equilibrium constant
ounitless, its an activity
o
o
equilibrium constant = (concentration of products (M)) / (concentration of
reactants (M))
instead of concentration, partial pressures can be used. that would be Kp
(if gas) and instead of Molar, Pressure is used
treat liquids and solids as constants; they are not part of the concentration
only gas and aqueous contributes to the equilibrium constant
o
o
partial pressure equilibrium constant = concentration equilibrium constant
(.0821T)^(moles of gaseous products - moles of gaseous reactants)
deriving this equation:
1
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Chem 1 C
oCombining K for multiple reactions
o
similar to hess's law, but not the same
Le Chatelier's principle
oif an external stress is applied to a system at equilibrium, the system adjusts in
such a way that the stress is partiall offset as the system reachers a new
equilibrium position
o
concentration changes
does not change equilibrium constant, only position
add more products (right) will cause the equilibrium to shift to the
left (reactants) because more reactants can be made
volume/pressure changes
does not change equilibrium constant, only position
pressure increase (volume decrease) favors will shift toward the
side w/a smaller # of net gaseous moles
2
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Chem 1 C
if both numbers r the same (i.e. one mole vs one mole) changing
pressure/volume does nothing to the equilibrium position
adding pressure w/other gasses does nothing
temperature changes
changes equilibrium constant
adding heat to an endothermic (delta H is +) process (that is, in one
direction) will cause the equilibrium constant to rise or fall
depending on the coefficient of the products and reactants and its
place in the concentration constant
ex: heat added to
AB --> 2CD is endothermic (detla H is +, with AB), so
adding heat to AB will make more CD and therefore the K
will increase
adding a catalyst
does not change equilibrium, just the rate it reaches it
Free energy and Equilibrium
o
o
change in free energy = -(8.31J/molK)(Temp)(lnK)
o
o
change in free energy = change in enthalpy - (temperature)(change in
entropy)
othose two equations combined makes von't Hoff exn
o
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Document Summary

Chem 1 c if both numbers r the same (i. e. one mole vs one mole) changing pressure/volume does nothing to the equilibrium position adding pressure w/other gasses does nothing temperature changes. Free energy and equilibrium change in free energy = -(8. 31j/molk)(temp)(lnk) change in free energy = change in enthalpy - (temperature)(change in entropy) those two equations combined makes von"t hoff exn. Log of the hydrogen ion concentration o: acid o, base o ph = -log[h3o+] = -log[h+] poh = -log[oh-] ph + poh = 14 ph = 6. 99- [h+] > 10^-7 denotes a photon or electron pair has a conjugate base ph = 7. 01+ [h+] < 10^-7 accepts a photon or electron pair has a conjugate acid. H3o+ is the strongest acid that can exist in an aqueous solution. Oh- is the strongest base that can exist in an aqueous solution o neutral o. Kw = [h+][oh-] = [h3o+][oh-] = 10^-14.