You'd need +6.79 kJ.
In order to determine how much heat is needed to melt that much cobalt at its melting point you need to know two things
- the mass of the sample;
- the heat of fusion,
#DeltaH_"fus"#, of cobalt.
A substance's enthalpy of fusion (heat of fusion) tells you how much energy is needed to convert one gram of that substance from solid to liquid, or given off when one gram is converted from liquid to solid.
Since you're essentially dealing with a phase change, the temperature of the sample will remain unchanged.
Notice that the value of
In other words, 15.5 kJ of heat are needed to melt 1 mole, not one gram, of cobalt at its melting point of
The equation you'll use looks like this
This means that you'll need
of heat to melt your sample.
Rounded to three sig figs, the answer will be