Mercury is a highly toxic metal. Although it is a liquid at room temperature, it has a high vapor pressure and a low enthalpy of vaporization (294 J/g). What quantity of heat energy transfer is required to vaporize 0.500 mL of mercury at 357 °C, its normal boiling point? The density of Hg (l ) is 13.6 g/mL. Compare this heat energy transfer with the amount needed to vaporize 0.500 mL water. See Table 11.2 for the molar enthalpy of vaporization of H2O.