Question

What amount of heat is required to melt `"300 g"` of ice at its freezing point if the enthalpy of fusion is `"6.02 kJ/mol"`?

Answer 1

For a phase transition, we assume a constant temperature (and also, pressure). So, the heat flow `q` into a substance is equal to the enthalpy change `DeltaH`.

`bb(q_P)`

`= bb(mDeltaH)`, if `DeltaH` is in `"J/g"`, or
`= nDeltaH = bb(m/(M_m)DeltaH)`, if `DeltaH` is in `"J/mol"`,

where:

• `m` is the mass of the ice in `"g"`.
• `n` is the `bb("mol")`s of the ice.
• `M_m` is the molar mass of the ice in `"g/mol"`.
• `DeltaH` is the enthalpy of fusion, which is about `"6.02 kJ/mol"` for ice at `0^@ "C"` and `"1 atm"`.

So, simply solve for the heat flow required to melt `"300 g"` of ice:

`color(blue)(q_P) = (300 cancel"g" xx cancel"1 mol"/(18.015 cancel"g"))("6.02 kJ"/cancel"mol")`

`=` `color(blue)("100. kJ")`