Entropy: things that affect entropy.


Entropy, S

Since endothermic reactions can occur spontaneously at room temp., enthalpy changes alone do not control whether reactions occur. We must consider entropy.

The second law of thermodynamics states that spontaneous changes result in an increase in disorder or entropy. This law determines:

  • whether a physical/chemical change is likely to happen at a particular temp
  • whether redox reactions will take place
  • the position of equilibrium

Things that affect entropy:

Physical State

  • entropy increases from solid to gas: solid < liquid < gas
  • It follows that the entropy of perfect crystals at zero kelvin is zero. (3rd law of thermodynamics)


  • quanta are fixed 'packages' of energy
  • The more energy


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