When it snows in the winter, we can sometimes see that some street cleaners scatter strange white powder on the road. A few minutes after they spread it out, the snow surprisingly begins to melt! The cause of this amazing phenomenon is the white powder on the snow, called Calcium Chloride (CaCl2). Calcium Chloride has some fascinating properties that are very appropriate for melting snow. Due to this fact, Calcium Chloride is known as a great revolution of the de-icing agent. Through this article, I will talk about how these interesting properties melt the snow.
The first property: relationship with the water
Calcium Chloride possesses a property, which absorbs moisture from the surrounding air and is dissolved in water, called “deliquescence”. Since it has high deliquescence, Calcium Chloride can contain the water vapor, so a chemical reaction between the Calcium Chloride and the water can easily occur. Surprisingly, since the solubility of Calcium Chloride is very high, 74.5g/100mL at 20 degrees Celsius, this reaction can produce a significant amount of aqueous Calcium Chloride solution. With this high solubility and deliquescence, Calcium Chloride can absorb the water from the snow on the ground.
The second property: an exothermic or endothermic reaction?
There are two types of reactions: endothermic reactions and exothermic reactions. An endothermic reaction is a reaction taking the energy from outside of the system. Since the heat energy is taken away from the surroundings, the temperature is cooled down. Due to this transference, the energy of the substances produced has more energy.
By comparison, there is another type of reaction, called an exothermic reaction. An exothermic reaction is a reaction to release the energy to the surroundings, so the temperature outside of the system is heated up. Since the energy is given away through the reaction, less energy is in the produced materials.
Through the reaction between CaCl2 and the water, by making the aqueous CaCl2 solution, CaCl2 and the water are in a high energy state, but the solution is in a low energy state. Due to this difference, the reaction is exothermic so it releases energy to the environment, which is the snow in this situation. Since the heat energy is released into the snow, the temperature of the snow increases, so the snow begins to melt.
The Third property: freezing point depression
Due to the chemical reaction above, the snow currently looks like a liquid. However, it could be frozen again, but it does not actually happen. This is because of freezing point depression. To change a state of matter from liquid to solid, called freezing, a certain temperature is required to condense the particles in the liquid. The normal freezing point of pure water is 0 degrees Celsius, but if the water becomes the mixture, the normal freezing point significantly decreases.
How can this freezing point lower? Firstly, the mixture produced would have a lower vapor pressure than that of pure ice at 0 celsius. However, as the temperature decreases, the vapor pressure of ice decreases more quickly than that of the solution. Then the new freezing point can be established when the vapor pressure of the ice equals the vapor pressure of the solution (mixture). As a result, the freezing point of the mixture can be less than 0 degrees celsius.
Conclusion
Even though Calcium Chloride has a marvelous deicing ability for these three main reasons, it has some serious problems for the environment: products based on Chloride remove Oxygen gas from the water and are very corrosive to the metal. For these harmful impacts, the use of this material needs to be decreased. However, there is a fascinating alternative: starfish deicer! Compared with other deicers like Calcium Chloride, this deicer can show better performance to melt snow and have less effect on the environment. This will be a fascinating alternative for Calcium Chloride!
Reference
Book: Chemistry: Zumdahl
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