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A Cool Change

This time, we are going to look into the sciences of chemistry and energy. It may seem strange to be looking into two different areas of science, but it is not unusual for the areas of science to overlap.

You will need:

  • two glasses of water
  • epsom salts
  • a spoon
  • a thermometer

Place the two glasses of water on the table, and let them sit for a few minutes. Use the thermometer to check the temperature of both glasses of water. You want them both to be the same temperature.

Next, place a tablespoon of epsom salts into one of the glasses of water, and stir. Wait a minute and then test the temperature of the two glasses again. Are they still the same?

You probably found that the water with the epsom salts is a little cooler. Wait another minute and test it again. It should be even cooler. Over a period of a few minutes, I found that the temperature of the water with the epsom salts dropped over two degrees. Why?

Change is tied to energy. Whenever something changes, energy has to be involved, and that includes chemical processes. We often think of chemical reactions as giving off heat, and many of them do. These changes are exothermic, meaning "outside heating", because they give off heat.

But sometimes a change can be endothermic, which means that heat is absorbed from surrounding materials, making them cooler.

The chemical formula for epsom salts is MgSO4·7H2O. When it dissolves in water, it separates into magnesium ions (Mg) and sulfate ions (SO4). For them to separate, they need to absorb some energy, in this case heat energy, which is absorbed from the surrounding water, making it cooler.

The same thing happens with other chemicals, including ammonium nitrate, which is used in "instant cold" packs. With cold packs, you simply add water. The ammonium nitrate is endothermic as it dissolves in water, and the pack gets cold enough to sooth an injury.

Have a wonder-filled week.