Physical changes occur when the form of a chemical substance changes but its chemical composition remains intact. Phase changes are one type of physical change. The substance moves from solid to liquid to gas form. While the substance may look or behave differently, the chemical composition of the substance remains the same.
What Are Gases? A gas is one of the three primary states of matter, along with solids and liquids. Gases are characterized by the fact that they have no fixed shape and no fixed volume. In the gaseous state, the particles have a lot of energy. They bounce around, collide with one another and have a lot of space between them. If gases are not confined to a sealed container, they will disperse freely into the atmosphere. Gases are the same molecules as those in the solid and liquid state, they are simply more loosely packed together.
How Does Condensation Occur? Temperature has a great effect on the state of a substance. At higher temperatures, substances boil and turn into gases. However, as the temperature cools, the energy of the particles reduces and the particles begin to slow down. As they slow down, they begin to move closer together and stick to one another. This process of moving from the gaseous phase to the liquid phase is known as condensation. By further lowering the temperature and reducing the amount of energy between the particles, the substance begins to form a solid. The process of moving from liquid to solid is known as freezing.
What Is the Condensation Point? The condensation point is the temperature at which the substance moves from a gas to a liquid. The condensation point is equivalent to its boiling point. As a temperature increases, the energy increases and the particles begin to move faster. Once it reaches the boiling point, it transforms from a liquid to a gas in a process known as evaporation or vaporization. The same is true in reverse. By bringing the temperature back down, the energy decreases and particles move slower. Once it reaches the boiling point and moves lower, the substance transforms back into a liquid. For water, this occurs at 212 degrees Fahrenheit or 100 degrees Celsius; however, other substances boil and condense at different temperatures.
Can Gases Go Directly to the Solid State? There are some instances where a substance moves directly from the gas phase to the solid phase without first becoming a liquid. This process is known as deposition. An example of this would be steam on a freezing cold day. If a person exhales onto a freezing cold window pane, the gas released from the lungs that comes in contact with the window pane would instantly crystallize or solidify without first becoming a liquid. The opposite process, moving from solid to gas, is known as sublimation. A common example of this process is dry ice. At room temperature, the solid carbon dioxide turns into a gas, creating a smoky or foggy effect.Learn more about States of Matter