Final answer:
The statement that high temperatures cause water molecules to expand is true, due to the phenomenon of thermal expansion which leads to increased intermolecular distances and a reduction in water density.
Step-by-step explanation:
The statement that high temperatures can cause water molecules to expand is true. When we discuss the expansion of water molecules, we're referring to the phenomenon of thermal expansion, where an increase in temperature can cause intermolecular distances to increase. As temperature rises, the molecules within water move more rapidly and the amplitude of their thermal motions also increases. This more energetic movement results in a greater average distance between the molecules, leading to a reduction in the density of the liquid; this is what's known as ordinary thermal expansion.
It's important to note that at temperatures around 4°C, water reaches its maximum density due to the competing effects of hydrogen bonding and thermal expansion. But overall, higher temperatures will lead to the expansion of water molecules, manifesting as an expansion in the volume of water. This is a concept that's critical within various areas of physics and engineering.