Entropy of fusion

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The entropy of fusion (symbol S M0 or Δ FUS S ) of a chemical substance is the entropy of this substance in case of change of the aggregate state from solid to liquid. If the value of the entropy of melt relates to the amount of substance of one mole , one also speaks of the molar entropy of melt (symbol S M0m ).

The unit of measurement for molar entropy of fusion is J / (K · mol).

As a measure of the disorder in a system, one can imagine that this disorder increases with increasing temperature - just like water molecules , which are initially in a certain order in the ice crystal , detach themselves from this association when heated in liquid water until they dissolve move around almost completely independently of each other during boiling.

A formulation of the third law of thermodynamics says: For every pure substance that crystallizes in an ideal order, the entropy at absolute zero is the same. These substances are given  zero entropy at T = 0.

Therefore, molar entropies of melting can be given in absolute values. However, depending on the system under consideration, other zero points are chosen for the melt entropy. For electrochemical measurements in aqueous solutions containing ions , e.g. B. one assigns the proton the melting entropy zero.

Melting entropy and melting enthalpy are related via the equation T m  = Δ H / Δ S.

material Spec. Heat of fusion in kJ / mol Entropy of melting in J / (mol K)
aluminum 10.7 11.5
antimony 19.8 21.9
Bismuth 11.5 21.1
lead 4.85 8.1
cadmium 6.2 10.4
chrome 16.93 7.8
iron 15.0 8.3
gold 12.4 9.3
graphite 201 approx. 50.0
potassium 2.5 7.4
Cobalt 17.2 9.7
Carbon dioxide 7.9 36.5
copper 13.3 9.8
magnesium 9.1 9.9
manganese 14.5 9.5
sodium 2.6 7.0
nickel 17.7 10.2
platinum 19.5 9.6
mercury 2.37 10.1
oxygen 0.2 3.6
Sulfur (monoclinic) 1.2 3.1
silver 11.3 9.2
Silicon 50.66 30.1
water 6.01 22.0
hydrogen 0.06 4.3
tungsten 35.2 9.5
zinc 7.4 10.7
tin 7.03 13.9

See also

Web links

Individual evidence

  1. Walter J. Moore: Fundamentals of physical chemistry. de Gruyter, Berlin et al. 1990, ISBN 3-11-009941-1 .
  2. Peter R. Sahm , Ivan Egry, Thomas Volkmann (eds.): Melt, solidification, boundary surfaces. An introduction to the physics and technology of liquid and solid metals. Vieweg et al., Braunschweig et al. 1999, ISBN 3-540-41566-1 .