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Thermodynamics and Kinetics

rename
Updated 2009-06-05 19:50

Thermodynamics and Kinetics

 

The following tables were made using information in the following references:

 

Smith's Organic Chemistry ISBN=978-0-07-304986-1 or 978-0-07-304986-7.

McMurry's ISBN=0-13-187748-8.

 

Items marked with ? need checking.

 

TermMeaning
Ttemperature in Kelvin
Henthalpy
Sentropy
GGibbs Free Energy
ΔHchange in enthalpy
ΔSchange in entropy
ΔGchange in Gibbs Free Energy
ΔGΔH-TΔS
memorize

 

TermMeaning
ΔHenergy of bonds formed in products - energy of bonds broken in reactants ?
ΔHsum of ΔH's of bonds broken in reactants - sum of ΔH's of bonds formed in products ?
ΔH<0products have stronger bonds than reactants ?
ΔH<0favors product formation for small T
ΔH>0endothermic reaction
ΔH>0heat is a reactact
ΔH>0absorbs heat
ΔH>0reaction favored at high temperature ?
ΔH<0exothermic reaction
ΔH<0heat is a product
ΔH<0releases heat
ΔH<0reaction favored at low temperature
memorize

 

TermMeaning
low entropysolids
high entropygases
ΔS>0for solid to liquid or liquid to gas
ΔS<0for gas to liquid or liquid to solid
ΔS>0for less moles of reactants than products
ΔS<0for more moles of reactants than products
ΔS>0if disorder rises
ΔS<0if disorder falls
ΔS>0favors product formation
ΔS>0products have more disorder than reactants
ΔS<0products are more ordered than reactants
S for the universeit always rises
ΔS for the universealways positive
memorize

 

TermMeaning
ΔG<0spontaneous
ΔG<0releases Free Energy
ΔG<0exergonic process
ΔG>0non-spontaneous
ΔG>0absorbs Free Energy
ΔG>0endergonic process
ΔG>0more stable reactants
ΔG<0more stable products
ΔGsum of G's for products - sum of G's for reactants
ΔG-RT ln K
ΔG<0favors product formation
memorize

 

TermMeaning
EaActivation Energy
Eaalways positive
big Easlow reaction
small Eafast reaction
high concentrationfast reaction
high temperaturefast reaction
kineticshow fast reactions occur. reaction rates.
thermodynamicsenergies and equilibrium values
catalystalters Ea but not ΔG,ΔH,K
catalystalters kinetics but not thermodynamics
catalystalters the rate equilibrium is established
catalystdoes not alter equilibrium values
high pressurefavors side of reaction with less moles of gas
low pressurefavors side of reaction with more moles of gas
raise concentration of reactantsfavors forward reaction
lower concentration of productsfavors forward reaction
raise concentration of productsfavors reverse reaction
lower concentration of reactantsfavors reverse reaction
memorize

 

TermMeaning
Kequilibrium constant
Kconcentrations of products / concentrations of reactants
K([M]m [N]n)/([A]a [B]b)
for the reaction a A + b B <=> m M + n N
K>1favors products at equilibrium
K<1favors reactants at equilibrium
K<<1virtually no reaction occurs
K<0.001virtually no reaction occurs
K>>1reaction practically goes to completion
K>1000reaction practically goes to completion
memorize

 

What about Kc vs. Kp for gas reactions? For the reaction a A + b B <=> m M + n N aren't they:

 

Kc=(Mm Nn)/(Aa Bb)

 

Kp=(PMm PNn)/(PAa PBb)

 

where PM is the partial pressure of the gas M, and

 

PM=MRT

 

  by the ideal gas law. This gives:

 

Kp=Kc(RT)m+n-a-b

 

For the reaction a A + b B <=> m M + n N, what are the rates in the forward and reverse directions? Aren't they like below ?

 

-1/a dA/dt = -1/b dB/dt = 1/m dM/dt = 1/n dN/dt = k1 Aa Bb - k2 Mm Nn

 

It would be good to add 0th, 1st, and 2nd order reaction kinetics here too.

 

Also discuss the relationship between the equilibrium constant and the forward and reverse rates of a reaction.