Which Is Faster: Melting Ice in Water or Air?

If you took the time to watch ice cubes melt, it might be hard to tell whether they melted faster in water or air, however, if the water and air are at the same temperature, ice melts more quickly in one than in the other.

Why Ice Melts at Different Rates in Air and Water

Assuming the air and water are both the same temperature, ice usually melts more quickly in water. This is because the molecules in water are more tightly packed than the molecules in the air, allowing more contact with the ice and a greater rate of heat transfer. There's increased active surface area when ice is in a liquid as opposed when it's surrounded by a gas. Water has a higher heat capacity than air, which means the different chemical compositions of the two materials also matter.

Complicating Factors

The melting of ice is complicated by several things. Initially, the surface area of ice melting in air and ice melting in water is the same, but as the ice melts in air, a thin layer of water results. This layer absorbs some of the heat from the air and has a slight insulating effect on the remaining ice.

When you melt an ice cube in a cup of water, it's exposed to both air and water. The part of the ice cube in the water melts faster than the ice in the air, but as the ice cube melts, it sinks further down. If you supported the ice to prevent it from sinking, you could see the portion of the ice in the water would melt more quickly than the part in the air.

Other factors come can into play as well: If the air is blowing across the ice cube, the increased circulation may allow the ice to melt faster in air than in water. If the air and water are different temperatures, the ice may melt more quickly in the medium with the higher temperature.

Ice-Melting Experiment

The best way to answer a scientific question is to perform your own experiment, which can yield surprising results. For example, hot water can sometimes freeze faster than cold water. To conduct your own ice-melting experiment, follow these steps:

1. Freeze two ice cubes. Ensure that the cubes are the same size and shape and made from the same water source. The size, shape, and purity of water affect how quickly ice melts, so you don't want to complicate the experiment with these variables.
2. Fill a container of water and give it time to reach room temperature. Do you think the size of the container (the volume of water) will affect your experiment?
3. Place one ice cube in the water and the other on a room-temperature surface. See which ice cube melts first.

The surface on which you place the ice cube will also affect the results. If you were in microgravity—like on a space station—you might be able to get better data because the ice cube would be floating in the air.