At this point, we are all too familiar with the snow that surrounds us. Those of us who spend time driving also know the snow to be the reason that the roads deteriorate so much each winter. Snow falls and covers the roads. Then, the snow melts on the roads because of the heat of continual driving (addition of kinetic energy) and seeps into small cracks in the pavement. Temperatures then drop and the water that melted from the snow in the cracks of the pavement expands as explained in the Brown chapter. When it freezes, water expands. Ice is of a lower density than water and thus takes up more space as the molecules stop moving. This freezing causes cracks and potholes to form and grow as the water beneath the surface of the pavement expands and contracts as the temperature varies.
I also looked into why salt is used during the winter to prevent the formation of ice. Salt lowers the freezing point of water, 32°F/ 0°C. If salt is added, that temperature drops. This is one of the reasons that we don’t see the ocean or salty rivers freezing as quickly or easily as fresh bodies of water. Road salt is polar and thus can be dissolved by water (since water is polar and likes dissolve likes) and will lower its freezing point. A water solution that is 10% salt will freeze at 20°F or -6°C and 20% saline will freeze at 2°F or -16°C—each additional 10% will result in a 10°C cooler freezing temperature.
It is interesting how these two phenomena can be explained by what we learned in class and read about over the past week. I’d be interested to know more about how different pressures affect these phenomena if at all.
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