Question: how much heat is needed to vaporize 100g of water at 100◦c?
Answer: The enthalpy of vaporization of water is 2256.4J/g, meaning that 2256.4J of heat are required to convert 1g of water at 100C to steam at 100C. In this case, we have 100g of water at 100C and we want to vaporize it to steam (also at 100C). This requires ΔH = 2256.4(100) = 225,640J or 225.64kJ of heat energy.