A coil of current-carrying Nichrome wire is immersed in a liquid. (Ni chrome is a nickel chromium-iron alloy commonly used in heating elements.) When the potential difference across the coil is 12 V and the current through the coil is 5.2 A, the liquid evaporates at the steady rate of 21, mg/s. Calculate the heat of vaporization of the liquid (see Section 18-8).