Free Energy and Entropy

Sontaneous changes:

  • occur in 1 particular direction and not the other
  • Exothermic reactions are usually spontaneous because they release nergy by going from a higher enthalpy to a lower enthalpy
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Free Energy (G)

A reaction is only spontaneous if it can do work, it must generate free energy

  • -ve /\G : means the reaction is spontaneous. /\(G)<0
  • +ve /\G : means the reaction is non-spontaneous, however it is spontaneous in the reverse direction. for  this kind of reaction, /\G >0
  • /\G=0 : This means that the system is in equilibrium
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Entropy (S)

Entropy is a measure of the disorder of a system

  • the greater the amount of disoder, the higher the value of the entropy (S)
  • the units for entropy are joules per mole kelvin (J/m/K)

The Equation for entropy change is

  • Entropy change= Final Entropy - Initial Entropy
  • /\S = S(final) - S(initial)
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Free Energy, Entropy and Enthalpy

Free enregy and Entropy are linked by the equation:

/\G = /\H - T/\S            

were /\H= Enthalpy change      and T= temperature in K

When a system is in equiilibrium, the free energy change is equal to 0 /\G = 0

this means that /\H - T/\S = 0

/\H = T/\S     and therefore /\S = /\H / T

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