What is the equation for the calculation of heat of fusion?

1 Answer
Truong-Son N.
Jul 21, 2018

The enthalpy of fusion, DeltaH_"fus", is a measured quantity, also known as the latent heat of fusion, but it is not the same as q_"fus", the heat flow that causes melting or freezing to occur.

The only "equation" that utilizes q_"fus" in general chemistry is:

q_"fus" = pmnDeltaH_"fus"

  • q_"fus" is the heat flow at constant atmospheric pressure, that pertains to either melting or freezing. Here it is in units of "kJ".
  • n is the mols of liquid being freezed, or the mols of solid being melted.
  • DeltaH_"fus" is the enthalpy of fusion, and is a positive quantity usually reported in "kJ/mol".

The pm is assigned depending on the direction of heat flow... if one wishes to melt a solid,

q_"fus" -= q_"melt" = nDeltaH_"fus"

If one wishes to freeze a liquid...

q_"fus" -= q_"freeze" = -nDeltaH_"fus"

And this is because the object is the system... so

  • heat flowing in to melt it must be given a positive sign, for the system gains heat to melt.
  • heat flowing out to freeze it must be given a negative sign, for the system loses heat to freeze.
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