Question

How is `DeltaH_(fusion)` used to calculate the mass of solid that 1kJ of energy will melt?

Answer 1

With no need of a formula. Is `DeltabarH_"fus"` positive or negative for melting?

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Given the enthalpy of fusion, simple unit conversion gives:

`overbrace("kJ"/"mol")^(DeltabarH_"tr") xx overbrace("mol"/"g" xx "g")^(m_"solid"//M_"solid") = overbrace("kJ")^(q)`

where `DeltabarH_"tr"` is the molar enthalpy of phase transition in `"kJ/mol"`, `q` is heat flow in `"kJ"`, `m` is mass in `"g"`, and `M` is molar mass in `"g/mol"`.

Thus:

`"g" = overbrace(cancel"kJ")^(q) xx overbrace(cancel"mol"/cancel"kJ")^(DeltabarH_"fus"^(-1)) xx overbrace("g"/cancel"mol")^(M_"solid"^(-1))`

And yet, this still refers to a real equation that we could have invoked only at constant pressure:

`q = nDeltabarH_"tr"`

where `n` is the mols of substance and `DeltabarH_"tr"` is its molar enthalpy of phase transition.