Identify one phase change you would see in a root beer float and describe what causes this change.

One phase change we would see in a root beer float is the change from liquid to gas.

Explanation:

In root beer float we can see all three states: solid, liquid and gas. Solid being the ice cream, beer as the liquid and the reaction after mixing the creates the gas. As we mix ice cream (solid) and beer (liquid) in a glass then the bubble formation process occurs which is called as carbonation creating the gas. Hence root beer float is a simple experiment showing all three states and change in phase from solid and liquid into gas.