# What is the formula for #DeltaH_"fus"#?

##### 1 Answer

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

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

#q# is theheat flowthrough the system atconstant pressureand the same temperature.#n_"substance"# is the#\mathbf("mol")# s of the substanceat hand that is transitioning to a new phase.

If you were looking at water freezing/melting, then

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

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

#=# #color(blue)("6.02 kJ")# of heatabsorbedtomeltit, orreleasedwhenfreezingit.