In this investigation, students test evaporation rates for different liquids. Next, students use a thermometer to measure the temperature change during evaporation. Students will explore the energy change associated with evaporation and the differences in evaporation rates of different liquids.
Because water can take a long time to evaporate, you may wish to have students move on to the second part of the investigation after recording evaporation times for acetone and isopropyl alcohol. Note that evaporation times may vary according to humidity and air currents. Integrating into the Curriculum This investigation could be incorporated into a unit on phase changes, chemical and physical changes, and energy.
In this activity, you will explore the energy change that accompanies the process of evaporation. Evaporation, like melting or freezing, is an example of a phase change —a change from one physical form of a substance to another. During evaporation, energetic molecules leave the liquid phase, which lowers the average energy of the remaining liquid molecules. The remaining liquid molecules can then absorb energy from their surroundings. This process can take place at any temperature because some of the molecules in a liquid will always have enough energy to enter the gas phase.
Phase changes release or use energy because they bring particles closer together or cause them to move farther apart. To understand why these processes release or use energy, recall that all atoms or ions have at least some attraction for one another.
Overcoming these attractions, as particles move farther apart, requires energy. When particles come back together, energy is released. During a phase change, the attractive forces between whole molecules are disrupted or restored. These are called intermolecular forces. Conversely, during a chemical change, the bonds between atoms within a molecule or ion are disrupted or restored.
These are called intramolecular forces. The relative strength of the intermolecular forces of a substance determines how much energy is required for two molecules of that substance to move further apart. Substances with very strong intermolecular forces like water require a comparatively greater amount of energy to separate. For example, a great deal of energy is needed to convert liquid water to water vapor because water molecules have a particularly strong form of intermolecular attraction called hydrogen bonding.
The energy added to the liquid water has to be enough to overcome the attraction that individual water molecules have for one another. The molecules of other liquids, however, may not be as strongly attracted to one another as water molecules are, and therefore require less energy to vaporize.
You can visualize the energy implications of phase changes using energy diagrams like the ones shown below. The horizontal lines represent the energies of substances in particular states. The higher horizontal line represents a substance in a physical state at a higher energy level, and the lower horizontal line represents a substance in a physical state at a lower energy level.
The diagram on the left shows energy being absorbed by water molecules as it would be when ice melts to form liquid water.
The energy diagram on the right shows energy being released from water molecules as it would be when liquid water freezes to form ice. But where does the energy needed to melt ice come from? Where does the energy released as ice is formed go? Energy may be absorbed from the surroundings to provide the energy needed to melt ice, or the surroundings may receive the energy released when water freezes.
In the examples above, the surroundings can be defined as everything other than the water molecules involved in these phase changes. The water molecules are the system —the molecules we are studying. If no button appears, you cannot download or save the media.
Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. The movement of water throughout Earth can be understood as a cycle where H20 moves from one state of matter to another. Use these standards-aligned resources to teach middle schoolers more about condensation, precipitation, and weather patterns that are affected by, and a part of, the water cycle.
The water cycle describes how water is exchanged cycled through Earth's land, ocean, and atmosphere. The water cycle is the endless process that connects all of the water on Earth. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image Evaporation on a Farm Water evaporates from a sugar beet field after a summer shower in Borger, Netherlands.
Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Text Text on this page is printable and can be used according to our Terms of Service. Interactives Any interactives on this page can only be played while you are visiting our website. Related Resources. The Water Cycle. View Collection. The atmosphere is the superhighway in the sky that moves water everywhere over the Earth. Water at the Earth's surface evaporates into water vapor which rises up into the sky to become part of a cloud which will float off with the winds, eventually releasing water back to Earth as precipitation.
The air is full of water, as water vapor, even if you can't see it. Condensation is the process of water vapor turning back into liquid water, with the best example being those big, fluffy clouds floating over your head. And when the water droplets in clouds combine, they become heavy enough to form raindrops to rain down onto your head. You can't see it, but a large portion of the world's freshwater lies underground. It may all start as precipitation, but through infiltration and seepage, water soaks into the ground in vast amounts.
Water in the ground keeps all plant life alive and serves peoples' needs, too. Note: This section of the Water Science School discusses the Earth's "natural" water cycle without human Runoff is nothing more than water "running off" the land surface. Just as the water you wash your car with runs off down the driveway as you work, the rain that Mother Nature covers the landscape with runs off downhill, too due to gravity.
Runoff is an important component of the natural water cycle. Solid, liquid, and gas - the three states of water. We see water freeze and turn to ice and we see water evaporate and turn to gas but This process is called sublimation and you can read all about it below. Skip to main content. Search Search. Water Science School. Evaporation and the Water Cycle. Downloadable Water Cycle Products coming soon! Printable versions of our water-cycle diagrams and products.
Science Center Objects Overview Related Science For the water cycle to work, water has to get from the Earth's surface back up into the skies so it can rain back down and ruin your parade or water your crops or yard.
Your table salt might have come from an evaporation pond. Credit: Wikipedia, Creative Commons. Credit: Wikimedia , Creative Commons. Below are other science topics associated with the water cycle. Date published: July 10, Filter Total Items: Year Select Year Apply Filter.
Date published: November 6, Note: This section of the Water Science School Date published: September 8, Date published: July 16, Date published: June 12,
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