Download Heating Curve of Water: Phases, Heat Capacity, and Latent Heats and more Slides Chemistry in PDF only on Docsity!
THE HEATING CURVE OF WATER
Now let's look at a schematic diagram of continuous heating of water from a temperature well below the freezing point to one well above the vaporization point. Temperature of a sample of water is plotted vs. heat added at a constant rate. This is an amazing curve and one worth staring at for a while.
Let's trace that curve from left to right across five regions. Note that on the bottom axis we're just adding heat to the sample at a steady rate, but what is happening to the temperature is anything but steady.
(1) Heating the solid
As we add heat to ice, its temperature rises. That's no big surprise. It rises at a linear rate that is governed by the heat capacity of ice, something that can be looked up in a table.
(2) 0˚C
What happens at 0˚C is really remarkable. We add heat but the temperature does not increase, even after a substantial amount of heat is added. That's a very strange result. Imagine if you were the first to discover it. People might not believe you!
What is happening, of course, is that ice is undergoing a phase transition : ice → liquid. It turns out that this phase transition alone, without rise in temperature, requires an extra amount of heat that we call the latent heat of fusion , ΔHf. Mathematically, the heat capacity of water at this temperature (and at 100˚C) is infinite.
(3) 0˚C - 100˚C Heating the liquid
After the solid melts to liquid, the liquid reflects added heat as a rise in its temperature. The slope of the rise isn't quite the same as that of the solid because the heat capacity of water is a little different that that of ice (see table underHeat).
