What is the formula for DeltaH_"fus"?

1 Answer
Truong-Son N.
Aug 12, 2016

Enthalpy of fusion (or really, enthalpy of phase transitions) is a constant-pressure heat flow. So you can work it out just from knowing that and the units.

The molar enthalpy of (common) phase transitions (that is, in "kJ/mol") would be:

\mathbf(DeltabarH_"trs" = q_p/(n_"substance"))

where:

  • q is the heat flow through the system at constant pressure and the same temperature.
  • n_"substance" is the \mathbf("mol")s of the substance at hand that is transitioning to a new phase.

If you were looking at water freezing/melting, then DeltabarH_"fus" ~~ "6.02 kJ/mol". That means if you had "1 mol" of water, then you would have

color(blue)(q_p) = n_"substance" xx DeltabarH_"fus"

= ("1 mol")("6.02 kJ/mol")

= color(blue)("6.02 kJ") of heat absorbed to melt it, or released when freezing it.

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