Why is so much energy used to heat or cool water?
Water's hydrogen bonds require energy to break the bonds so that the molecules can move more freely. and I believe for cooling, the attractions of the hydrogen bonds that are constantly breaking and reforming (pulling each molecule in random directions constantly) makes it so that it would require a lot of energy to be lost as heat for the average kinetic energy or temperature to drop.
Assuming you got that number off an electric kettle it is because that is how much power is needed to heat the water. The number of watts actually measure how much energy the kettle is designed to use. Water is very hard to heat compared to other liquids(or to cool). So it takes a lot of watts to get the kettle to heat the water.
Because water has a high "specific heat level". In short, it takes a lot of energy to raise the temperature of water there for it takes a long time and a lot of energy to raise water temps. Metal typically has a low "specific heat level" so it doesn't require much energy to raise or lower the temp so it happens much faster.
Yes, large bodies of water have a moderating effect on climate. Water has a higher heat capacity than the dry land, which is to say, it takes more energy to heat it up, and so in hot weather it takes longer for water to get hot, and in cold weather it then takes longer for water to cool off, since it stores so much heat energy. Coastal areas, therefore, benefit from this moderating influence. Inland…
Temperature is the average amount of energy present in something; heat is the net total. For example, you can have a glass of water and a pool of water that are the same temperature: dispersed throughout, the amount of energy in each substance is the same. However, in total the pool as much more energy, or heat, because it is much larger than the glass of water.
If you freeze water you are removing a particle's kinetic energy from the system that is in the form of heat energy. So as you heat up ice you are giving the water molecules more thermal kinetic energy so it transitions to water. If you keep pumping in heat (energy) these molecules will eventually have so much energy it will vaporize and turn to steam.
Oceans are large areas of water and water does not heat up or cool down as quickly as land does. The reason for this is that water has a higher specific heat than land; it takes more energy to raise the temperature of water than it does to raise the temperature of land. So areas along the coast tend to have weather that does not vary much.
You would have to specify the amount of each. If the volume is the same, water (having a larger density) would have a much larger mass, and therefore take much longer to cool down or heat up. Even for the same mass, water will take longer to cool down or heat up, because of its larger specific heat.