To calculate the standard enthalpy change for the fusion reaction of solid lithium at its melting point, we need to know the enthalpy of fusion Hfus for lithium. The enthalpy of fusion is the amount of energy required to change a substance from the solid phase to the liquid phase at constant temperature and pressure.For lithium, the enthalpy of fusion Hfus is 3.00 kJ/mol.The fusion reaction for lithium can be represented as:Li s Li l Since we are considering the reaction under standard conditions, we can directly use the enthalpy of fusion as the standard enthalpy change for the reaction.H = Hfus = 3.00 kJ/molSo, the standard enthalpy change for the fusion reaction of solid lithium at its melting point is 3.00 kJ/mol.