To calculate the amount of heat energy needed to melt the ice cube, we can use the formula:q = n * Hfwhere q is the heat energy, n is the number of moles of the substance, and Hf is the enthalpy of fusion.First, we need to find the number of moles n of the ice cube. The molar mass of water is 18.015 g/mol. n = mass / molar massn = 25 g / 18.015 g/moln 1.387 molesNow, we can use the formula to find the heat energy needed:q = n * Hfq = 1.387 moles * 6.01 kJ/molq 8.34 kJSo, the amount of heat energy needed to melt the 25-g ice cube at its melting point of 0C is approximately 8.34 kJ.