How many pieces of data do you need to get the enthalpy of fusion of copper? The heat capacity of copper is #"0.385 J/g"^@ "C"#.

1 Answer
Truong-Son N.
Oct 1, 2017

Well, more than one, that's for sure.

And you would need the mass #m# as well as the enthalpy of fusion, #DeltaH_"fus"#. You may also need the molar mass of copper, if you were only given the mass...

Usual phase transitions are done at constant temperature, and thus, there is no specific heat capacity involved in the calculation here. That would be a common error to make.

At constant pressure,

#q = DeltaH#,

if both are in #"J"# or both in #"kJ"#,

and we exploit this relationship at constant temperature and pressure to find the heat flow involved:

#color(blue)(barul|stackrel(" ")(" "q = m/MDeltaH" ")|)#

where if #DeltaH# is in #"kJ/mol"# (as it usually is), then:

  • #q# is the heat flow went INTO the melting of copper in #"kJ"#.
  • #m# is the mass of copper in #"g"#.
  • #M# is the molar mass in #"g/mol"# of copper.

One can verify the units:

#"kJ" = cancel"g" xx cancel"mol"/cancel"g" xx "kJ"/cancel"mol"# #color(blue)sqrt""#

The actual value of #DeltaH_"fus"# is roughly #"13.03 kJ/mol"# from here. You may want to verify that this is correct.

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