Will the water melt the ice, the ice freeze the water, or neither (equal quantities and temperature)?
Energy must be removed from water at 273K to make it freeze, and by the same token, when ice at 273K melts, it absorbs energy. These happen without any change in temperature. The required energy is called the specific heat of fusion and it differs from one substance to another. Water has a relatively high heat of fusion. a) If the surroundings are warmer than 273K, then heat will flow into the mixture and gradually warm the water and melt the ice. b) If the surroundings are colder, than heat will gradually move out of the water and into the surrounding environment, and the water will freeze. If you try to insulate the container of water/ice, you will slow down the process, but since insulation is not perfect, some heat will flow thru it and either a) or b) will eventually happen. If, in theory, you could perfectly insulate your mixture, then a few molecules of water would always be freezing, balanced by a few molecules of ice melting, but the total amounts of each would remain unchange
