When steam condenses, the surrounding air is

Updated November 22, 2019

By A.P. Mentzer

Water changes between solid, liquid and gaseous states but does not leave the confines of Earth’s surface or atmosphere. Water changes through an endless cycle precipitation, evaporation and condensation. When water vapor condenses, it changes from a gas to a liquid.

Water in its gaseous state is called water vapor. When water vapor condenses, the molecules cool and change into a liquid state.

When water changes from one state of matter to another, the molecules spread apart or move more closely together. The water molecules in ice are packed closely together but are farther apart in liquid water. The molecules in water vapor are even more spread out. Solid ice has the greatest density and water vapor has the lowest density.

The change in density is accompanied by a release of energy when the molecules move closer together, such as when a gas becomes a liquid, or a liquid becomes a solid. When water changes from a solid to a liquid, or a liquid to a gas it absorbs energy from the environment and the molecules spread apart.

The water cycle allows Earth to maintain its water supply. Heat causes liquid water on Earth’s surface to evaporate and change into gaseous water vapor. Most water vapor in the atmosphere evaporates from bodies of water, especially the oceans. Evaporation occurs more quickly as temperature increases.

Humidity is the amount of water vapor in the air. When water vapor in the air cools, the opposite of evaporation occurs: condensation. The condensation definition is water changing from a gas to a liquid. Condensation makes it possible for clouds to form.

Clouds contain liquid water droplets and solid ice crystals. The cooler temperature at high altitudes causes more water vapor to condense. Water vapor condenses on minute particles of debris in the air which then collide with other condensed droplets nearby. Eventually the force of the collisions of these droplets of water causes precipitation to fall from the clouds to the ground and collecting in bodies of water.

The process in which water vapor turns into a liquid is called condensation. The gaseous water molecules release energy into the cooler air around them and move closer together. The spaces between the molecules decrease until they are close enough to change from a gas to a liquid.

When the air is warmer than the ground, water vapor condenses on ground surfaces to form dew. The temperature when dew forms is called the dew point. A similar effect occurs on the outer surface of a cold beverage, when air temperature is higher than the water in the glass.

Water condensation doesn’t always result in cloud formation at high altitudes. Water condenses whenever water vapor cools to a temperature lower than the point when evaporation occurs. Condensation happens near the ground when warm, humid air meets cooler land or water to create fog, which is like clouds that accumulate at ground level. Fog forms when the air temperature is equal to the dew point.

Some of the water vapor in the atmosphere that condenses is stored in clouds. Clouds are more likely to form when the air is humid and contains more water vapor. The energy released when gaseous water vapor condenses to form liquid water droplets is called latent heat. Latent heat from condensation causes an increase in air temperature surrounding the water droplets.

The warmer air rises, causing the water vapor to condense when it meets cooler air at a higher altitude. As more water vapor condenses, cloud volume increases, and the chance of precipitation increases. Instability occurs when clouds increase in height and are surrounded by warmer air. These conditions can trigger thunderstorms.

Liquid or frozen water falls to the surface as precipitation. It can be stored as solid particles in snow or ice or as a liquid in bodies of water. It remains in storage until it reaches the temperature when evaporation occurs, continuing the cycle.

No! The temperature of steam or water does NOT drop continuously when it cools. Let’s use the graph below to explain.

From the graph, when steam at 125°C cools, its temperature starts to drop (E) until it reaches 100 °C (D).  At 100 °C, the steam condenses and turns into liquid water. When all the steam is completely turned into liquid water, its temperature starts to drop again (C) until it reaches 0 °C. At 0 °C, the liquid water freezes and turns into ice (B). When all the liquid water is completely turned into ice, its temperature starts to drop again (A).

Why does steam (gas) form water (liquid) when it cools?

When steam cools, energy is removed from water molecules. As these molecules transfer their energy to the cooler surroundings, they move about much less, decreasing their kinetic energy. This decrease in kinetic energy cause water molecules to slightly stick together. Why would they stick together? They do because water molecules are polar. As a result of this polarity, water molecules stick together to form water when their kinetic energy significantly decrease.

How does kinetic energy vary when steam cools?

When steam cools, the kinetic energy of water molecules drops and the molecules move much less. Kinetic energy drops because water molecules transfer their energy to the colder surroundings. From the graph, regions of decreasing kinetic energy are: E, C, and A. However, at condensation and freezing points the kinetic energy and temperature stays constant.

What phase changes occur when steam cools and are these changes physical changes?

These phase changes are physical changes, and they are:

• Condensation at 100 °C, when water vapor (gas) turns into water (liquid water)
• Freezing at 0 °C, when liquid water turns into ice (solid water)

From the graph (cooling curve of water), you can see that the region at which water vapor condenses is longer than the region at which liquid water freezes. This means that much energy must be removed from steam to turn it into liquid water. From the graph, you can also see that

• water boils (boiling point) and condenses (condensation) at the same temperature
• melts (melting point) and freezes (freezing point) at the same temperature

Is energy conserved when water changes phases?

Yes, energy is conserved. The amount of energy we use to heat ice to turn to steam is the same amount of energy we get back when we cool that same steam back to ice. Thus, we say that energy is conserved.

To learn how temperature and kinetic energy vary as ice turns into steam, click here.