In general, it is not possible to determine if something has turned from a liquid to a gas or vice versa just by looking at it, without any additional information or observations. The transformation from a liquid to a gas, known as vaporization or evaporation, typically occurs at the boiling point of a substance, which is specific to that substance under a given set of conditions.
When a substance undergoes vaporization, its molecules gain enough energy to overcome the intermolecular forces holding them together in the liquid state. This energy allows the molecules to break free from the liquid's surface and enter the gas phase. However, this process is not directly observable through visual inspection alone.
There are some indirect visual cues that can suggest a phase change from liquid to gas, such as the appearance of bubbles or the formation of steam. Bubbles are commonly observed when a liquid is heated and reaches its boiling point, causing the gas phase to form within the liquid. Steam, which is composed of tiny water droplets suspended in the air, is often visible when water evaporates rapidly at its boiling point.
However, it's important to note that these visual cues are not definitive proof of a phase change, as substances can also release gases or produce bubbles through chemical reactions or other processes. To accurately determine if a substance has undergone a phase change, it is necessary to consider additional factors such as temperature, pressure, and knowledge of the substance's boiling point or vapor pressure. Experimental measurements or instruments may be required to provide more precise information about the state of a substance.