In: Mechanical Engineering
Vapor pressuer is the pressure exerted by the vapor on the liquid in thermodynamic equilibrium with it. Liquids boil when the Surrounding pressure falls below the vapor pressure.
Now consider water and the surrounding to be vacuum. the pressure exerted by the vacuum is zero, which is less than the vapor pressure and water will boil instantly irrespective of the temperature of the liquid.
The surface of moon has no atmosphere so no surrounding pressure and it could be considered similar case as that of vacuum so, water will boil instantly on surface of moon. The surface of the moon can have temperatures up to 150 deg C below zero and up to 120 deg C above zero. In both the cases water will boil instantly.