Visualizing the latent heat of fusion of ice

February 27th, 2012 by Charles Xie

Latent heat is the heat released or absorbed by an object during a change of state without the change of temperature. The latent heat of fusion is the energy absorbed when a substance melts or released when it freezes.

The two videos in this post present a visualization of the latent heat of fusion of ice. Three containers, one filled with brine, the other two with freshwater, were stored in a freezer for two days. The temperature of the freezer was enough to freeze the freshwater in the two containers but not the brine. They were then taken out and put on a foam board. The left one was the brine.

The first video shows the temperatures of the three containers shortly after salt was added to the middle one. The second video shows their temperatures after about an hour. Both videos show that the middle container was the coldest. Two factors contributed to the cooling of the middle container. One is the latent heat of the melting of ice due to the contact of salt. The other is the negative heat of solution of salt--that the dissolving of salt absorbs heat.

Initially, the brine container on the left was colder than the third container on the right. After an hour, the brine container became significantly warmer than the third container. What was cooling it? It is the latent heat of fusion due to the melting of ice in the container. Since the brine was in liquid state all the time, there was no latent heat involved and all the heat it absorbed from the room was used to increase its temperature.

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