Question

One day in a laboratory, some water spilled on a table. In just a few minutes the water had evaporated. Some days later, a similar amount of water spilled again. This time, the water remained on the table after 7 or 8 hours. Name three conditions that could have changed in the lab to cause this difference.

Short answer

The three conditions that could have changed to cause the difference in evaporation time are increased humidity, decreased temperature, and decreased air circulation in the laboratory.

Step-by-step solution

Identifying Variable - Humidity

The amount of moisture already present in the air, known as humidity, greatly influences the rate of evaporation. If the humidity in the lab was higher on the second day, the air would not have been able to accept as much moisture from the water spill, resulting in slower evaporation.

Identifying Variable - Temperature

Temperature is a key factor that affects evaporation. If the temperature in the lab was lower on the second day, the water molecules would have had less energy to convert from a liquid to a gaseous state, making the evaporation process slower.

Identifying Variable - Air Circulation

Air circulation or wind can also affect how quickly water evaporates. With increased air movement, water molecules are removed more quickly from the surface, speeding up evaporation. If there was less air circulation in the lab on the second day, the evaporation of the water spill would have been slower.

Key concepts

Humidity Influence on Evaporation

Understanding how humidity influences evaporation is crucial in establishing optimized laboratory conditions for various experiments. Humidity refers to the amount of water vapor present in the air. When the air is already saturated with moisture, it becomes harder for additional water to evaporate. The phenomenon can be compared to a crowded bus: when there's room, people can easily get on, but as it fills up, it becomes tough for more people to find a place.

During days with high humidity, the increased moisture content in the air inhibits additional water, such as our spilled water, from evaporating efficiently because the air cannot absorb much more water. In contrast, on a dry day with low humidity levels, the air can be likened to an almost empty bus, readily accepting new water molecules from the spill, leading to faster evaporation. This explains why the water on the table in the lab scenario took longer to evaporate on a day that was perhaps more humid compared to a day with drier conditions.

Temperature Effect on Evaporation

Temperature's role in the evaporation process is akin to lending energy to a party; the higher the temperature, the more energy is provided to the water molecules, which in turn increases their movement. This surge in energetic action means that more molecules can escape the liquid's surface tension and enter the air as vapor.

If we think of water molecules as dancers, then on the first day in the lab scenario, they might have had just the right tempo, perhaps a lively salsa, enabling them to energetically move from a liquid to a gaseous state. But on the second spill incident, the ‘dance’ might have been more of a slow waltz, due to a lower temperature. The slower rhythm would mean fewer molecules had the energy to break free, resulting in much slower evaporation rates.

Air Circulation and Evaporation

Air circulation is often the unsung hero in the process of evaporation. Imagine the surface of our water spill in the lab as a bustling marketplace of molecules. With good air circulation, akin to a series of open pathways or breezy winds through the marketplace, the air takes away the water vapor that forms as molecules leave the liquid phase. This movement makes way for more molecules to evaporate.

On a day with stagnant air—imagine a calm, windless market square—the vaporized molecules linger above the spill, creating a sort of ‘traffic jam,’ and thus, less room for other molecules to join the gaseous phase. This results in a slower rate of evaporation. When comparing the two occasions of the water spill in the lab, a day with proper ventilation or a fan would have promoted quicker evaporation versus a day with little to no air movement.