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1.4.1 entropy (HL)

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chem whatdriveschemicalreactions

Reactivity 1.4.1 - entropy, , is a measure of the dispersal or distribution of matter and/or energy in a system. the more ways the energy can be distributed, the higher the entropy. under the same conditions, the entropy of a gas is greater than that of a liquid, which in turn is greater than that of a solid

- entropy, , is a measure of the dispersal or distribution of matter and/or energy in a system.
- in other words, it is a measure of how disordered or chaotic a system is

  • when a system becomes more disordered, its entropy will increase
  • an increase in entropy means that the system becomes energetically more stable
  • chemical reactions will occur if the total entropy of the universe increases

the direction of natural or spontaneous change (change that occurs without the need to do work) is from low dispersal or entropy to high entropy.

the natural tendency of change can be reversed at the expense of doing work.

  • ordered states with small energy distribution are said to have low entropy
  • disordered states with a high energy distribution are said to have high entropy
predicting entropy changes
  • solids have the least entropy
  • liquids have middle
  • gases have the highest entropy
  • more substance means more entropy
absolute entropy

entropy depends on temperature and pressure, so entropy values refer to standard conditions and represented as

  • all entropy values are positive
  • a perfectly ordered solid at absolute 0 has an entropy of zero. all other states, which are more dispersed, have positive entropy values.
calculating entropy changes

  • entropy will change depending on the state of the matter

  • when calculating the coefficients used to balance the equation must be applied when calculating the overall entropy change

  • For example, when calculating the  for the reaction below we need to double the value for 

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