What happens to a sample of water when it is heated between 4 degrees c and 100 degrees c?

Answer 1

4 degrees celcius is the temperature at which water has it's highest density. As it goes lower towards freezing, it actually expands (one of waters most interesting and important attributes)

As you heat water from 4 degrees celcius, it gradually looses it's density, and steadily comes closer to crossing the threshold of boiling.

Fun fact:

Why is it that the bathroom is full of steam after i've showered, when the water wasn't nearly hot enough to be turning in to it's gas form (which it is generally concieved that water mulecules do once they reach 100 degrees celcius, and boiling starts)?

This is because energy in the mass of water as a whole, is not distributed evenly between the molecules.

As a consequence, some water will vaporize, even though most of the water still is far from doing so.

So to answer the rest of the question: as the water gradually rises in temperature, more and more water will have the nessecairy energy to vaporize.

And so, at some point, the vapor pressure of the liquid, is equal to the pressure exerted on it by the surrounding environmental pressure, and at that point, the water starts boiling.