Boiling of Water

Let’s consider heating a pound of water in a pan. Let’s go through step by step what happens to it, as we heat it. Along the way we will define some key technical terms.

Let’s say the water is at 70 deg F. If we heat it, its temperature rises. We can sense this rise in temperature on a thermometer. For example we transfer 10 BTUs to the water. Its temperature will rise to 80 deg F. We will be able to see this increase on a thermometer. Since we can sense this addition of heat, we call it the “Sensible Heat”.

Sensible Heat is defined as the heat received by a substance which results in temperature increase.

Let’s continue heating our pound of water. Gradually the water temperature will rise to 212 deg F. To raise the water’s temperature to 212 deg F, we will need to give it 172 BTUs (212 – 70 = 142).

212 deg F is a magic number for water. Let’s say you add 100 BTUs to the water just when it reaches 212 deg F. What happens?

Since the specific heat of water is 1.0, you expect the water temperature to rise by 100 deg to 312 deg F. Actually nothing happens. Water simply absorbs the heat and its temperature does not rise at all.