Evaporation
Evaporation describes the process of a liquid becoming a gas due to being heated. Liquids, gases, and solids can change their state due to the transfer of energy involved in a temperature change.
Suppose you’re teaching children about evaporation and how it works. In that case, we will explore this chemical process which refers to the heating of water molecules until they turn to vapor, to help you better understand and explain it. It all comes down to the amount of moisture, the temperature, and solar energy.
This state change can happen when the sun warms the surface of a body of water, and evaporation and condensation are natural processes in the Water Cycle. Humans heat water to create food and drinks and sometimes to purify water, as we have done for thousands of years.
When water gets so hot, it contains gas bubbles. This is called boiling or rapid vaporization rather than evaporation, whereas water becomes steam at a much slower rate when it is simmering. This is because the heat energy breaks the bonds between the water molecules.
Here are a few examples of everyday evaporation to help illustrate this process:
- Puddles outside disappearing
- Clothes drying on a line
- The water level going down in a cup
- Steam from a hot shower or bath
- Using a hairdryer
- Ironing clothes by heating moisture
- Floors and cars drying after cleaning
- Low rivers during hot weather
- Paint drying from a liquid
- Sweat evaporating from our bodies to cool us
This water hasn’t disappeared; it’s heated in the sun and is now floating in the air as vapor – which is much harder for us to see. However, when your breath looks misty in cold air, you can see this moisture because the vapor condenses as it loses heat energy.
Evaporation of a liquid continues until it reaches an equilibrium of evaporation and condensation or until the surrounding air is saturated with water vapor in an enclosed space.
Think about how the walls of a bathroom get wet from warm steam, which has evaporated, condensed on the cold wall, and will eventually evaporate back into the air as humidity. Humidity is the amount of water vapor in the air, and humans do it best when the air is at about 30 to 50% humidity.
You might refer to our page on condensation, which is the reverse of evaporation when water vapor cools and becomes liquid again. These are examples of changing states in chemistry, which is essential to learn for many other topics like studying the weather and cooking.Top of Form
Liquid to Gas – Changing States of Matter
Changes in the states of matter will also teach children about melting ice, why it snows, dissolving solids into liquids, where salt comes from, and more. You can discover so much about the world by studying the states of solids, drinks, and gases.
Evaporation and the Water Cycle
Evaporation is one of the four processes within the water cycle, alongside condensation, precipitation, and collection. On our planet, we have a constant amount of water that changes state depending on the conditions of the environment. In nature, water is constantly recycled between these states.
In this cycle, evaporation occurs when the sun heats water and causes the molecules to move faster and faster. Eventually, the water molecules move so quickly that they turn into gas. This gas is called water vapor. Once water vapor is formed, it spends about ten days floating around in the air and slowly but surely rises into the atmosphere.
Once the water vapor rises high enough, it begins to cool down. It then begins to condense and form larger water droplets. These larger and heavier water droplets then gather together to become clouds. Eventually, the clouds become so full of water that they release some forms of precipitation, such as rain or snow.
There are a variety of different places where water can evaporate from on the surface of the planet. Of course, much evaporation comes from the oceans, but water bodies such as lakes, rivers, and streams also contribute significantly towards the amount of water vapor in the atmosphere. The rest of the evaporated water comes from biological sources such as plants.
As stated above, the evaporation rate can vary depending on the conditions of the environment. Some of the main conditions that can affect this include:
- The humidity of the air
- The surface area of the liquid
- The temperature of the liquid
- The number of minerals dissolved in the liquid
- The flow rate of the air
- The pressure of the liquid
Practical uses for evaporation and the water cycle:
Evaporation and the water cycle are among Earth’s most important natural processes. Without them, we wouldn’t have rain, and Earth could quickly become uninhabitable.
But as well as this natural process, humans have found many other uses of evaporation and the water cycle.
For example, salt is made through the process of evaporation. Seawater naturally contains saline. When seawater is evaporated, the saline is too dense and heavy to travel upwards, so it remains on Earth, where it crystallizes to become salt.
Humans have manipulated this process for years by making relatively shallow ponds with large surface areas. The combination of the shallowness and the large surface area means that as much water in the pond is being heated up by the sun as possible, making evaporation faster.
As the water evaporates, it leaves behind salt, which is how table salt is made.
A fun and easy experiment you could try to test this is to fill a bowl with a bit of seawater and leave it out in the sun. Before too long, the water will have evaporated, and salt crystals will be left behind. This experiment is a great way to teach children about evaporation and the water cycle.
Teaching Ideas on Evaporation
You can help children’s understanding of this topic with images, slideshows, examples, and some hands-on activities.
Here are a few easy experiments you might like to run with your class or at home:
- Mark lines on a clear water container and checks the level over several days. Then, you can have a covered container for comparison.
- Hand up two matching wet clothes and a fan to blow air on one. Wind will speed up the drying process as water vapor is quickly carried away.
- Put some hand sanitizer on their hands and ask if their hands feel excellent from wet. Then get them to rub their hands until they dry. The alcohol gel has evaporated from their body heat, cooling (and cleaning) their hands in the process!
- Observe puddles on a rainy day, and check back to see if they get smaller after the rain has stopped. You can use cones to mark the edges.
- Boil water in a test tube or kettle so they can see the level going down as it turns to steam. Think about where the water ends up.
