when you add dry ice to water, it seems to boil. why is that?

You are then transfering heat from the liquid water to the solid dry ice, which sublimes gaseous CO2 into the water.

When you add dry ice to water, it appears to boil due to a process called sublimation. Dry ice is the solid form of carbon dioxide (CO2). Unlike most substances, dry ice does not melt into a liquid when it is heated. Instead, it undergoes sublimation, which means it transitions directly from a solid to a gas without becoming a liquid first.

In this case, when dry ice comes into contact with the water, it rapidly absorbs heat from the water. The temperature difference causes the dry ice to change from a solid state to a gaseous state, without passing through a liquid state. The process of sublimation releases carbon dioxide gas into the surrounding environment, giving the appearance of boiling.

To further understand why this happens, you need to know about heat transfer. Heat always flows from a higher-temperature object or substance to a lower-temperature one. In this case, when the dry ice absorbs heat from the water, the temperature of the water decreases, causing the phase change of dry ice to gas.

So, adding dry ice to water causes the water to transfer heat to the dry ice through conduction, resulting in the sublimation of the dry ice and the release of carbon dioxide gas. This gas then creates the bubbling or boiling effect that you observe.