Chem4Kids.com Home Page Matter Atoms Elements Reactions Biochemistry Activities Chem4kids Sections Search
States of Matter
 

Changing States of Matter

Phase changes happen as the temperature changes.

All matter can move from one state to another. It may require extreme temperatures or extreme pressures, but it can be done. Sometimes a substance doesn't want to change states. You have to use all of your tricks when that happens. To create a solid, you might have to decrease the temperature by a huge amount and then add pressure.

Some of you know about liquid nitrogen (N2). It is nitrogen from the atmosphere in a liquid form and it has to be super cold to stay a liquid. What if you wanted to turn it into a solid but couldn't make it cold enough to solidify? You could decrease the pressure in a vacuum chamber which lowers the boiling point. If you have a liquid like water at room temperature and you wanted a gas you could use a combination of high temperatures and low pressures to solve your problem.

Phase changes happen when certain points are reached. Sometimes a liquid wants to become a solid. Scientists use something called a freezing point to measure the temperature at which a liquid turns into a solid. There are physical effects that can change the freezing point. Pressure is one of those effects. When the pressure surrounding a substance goes up, the freezing point and other special points also go up. That means it's easier to keep things solid at higher pressures.

Generally solids are more dense than liquids because their molecules are closer together. The freezing process compacts the molecules into a smaller space. There are always exceptions in science. Water (H2O) is special on many levels. It has more space between its molecules when it is frozen. There's a whole expanding effect when the molecules organize into a solid state.

CHEMISTRY TERM PHASE CHANGE
Fusion (melting)
Freezing
Vaporization (boiling)
Condensation
Sublimation
Deposition
Solid to Liquid
Liquid to Solid
Liquid to Gas
Gas to Liquid
Solid to Gas
Gas to Solid

Solid to Liquid and Back to Solid

Adding energy to a solid can create a liquid.

Imagine that you are a solid. You're a cube of ice sitting on a counter. You dream of becoming liquid water. You need some energy. The atoms in a liquid have more energy than the atoms in a solid. Heat is probably the easiest energy you can use to change your physical state. There is a special temperature for every substance called the melting point. When a solid reaches the temperature of its melting point, it can become a liquid.

For water, the temperature has to be a little over zero degrees Celsius (0oC). If you were salt, sugar, or rock, your melting point would be higher than that of water. How do you know that? If their melting points were lower, they would be liquids at room temperature. The reverse of the melting process is called freezing. Liquid water freezes and becomes solid ice when the molecules lose energy.

Solid to Gas and Back to Solid

Water vapor can freeze at night and become frost on plants. You are used to solids melting and becoming liquids. Some of you may have also seen a solid become a gas. It's a process called sublimation. The easiest example of sublimation might be dry ice. Dry ice is solid carbon dioxide (CO2). Amazingly, when you leave dry ice out, it just turns into a gas. Have you ever heard of liquid carbon dioxide? It can be made, but not in normal situations. Coal is another example of a compound that will not melt at normal atmospheric pressures. It will sublimate at very high temperatures.

Can you go from a gas to a solid? Sure. It's called deposition when a gas becomes a solid without going through the liquid state of matter. Those of you who live near the equator may not have seen it, but closer to the poles we see frost on winter mornings. Those little frost crystals on plants build up when water vapor from the air becomes a solid on the leaves of plants.

More on Phase Changes in Part II...

Next Page on Matter
esta página en español
 
- Overview
- States
> Phase Change I
- Phase Change II
- Chemical-Physical
- Solids
- Liquids
- Evaporation
- Gases
- Plasmas
- BE Condensate
- Mixtures I
- Mixtures II
- Solutions I
- Solutions II
- Mixture Ex.

MORE CHEMISTRY TOPICS



Link to Cosmos4Kids.com Link to Biology4Kids.com Link to Chem4Kids.com Link to Geography4Kids.com Link to Physics4Kids.com Link to NumberNut.com Rader Network Side Navigation
 

Liquid Onboard the ISS (NASA/MSFC Video)
RETURN TO TOP
- or -

Matter Quiz

States of Matter Quiz

Keywords for Review

Antifreeze: Antifreeze is a substance which will lower the freezing point of water (H20) or another substance. You will often see antifreeze used in car engines in cold climates. When temperatures get below 0-degrees Celsius, the water in cooling systems is likely to freeze. When you add antifreeze, the solution will not freeze until a much lower temperature.

Crystals: A crystalline solid has a specific organization of molecules and atoms. These are the classic crystals of the world such as diamonds and all gemstones. They are often made up of specific molecules and have very structured geometric shapes. These solids also have more clearly defined melting points. Table salt (NaCl) would be a good example of a crystalline solid.

Density: Density is a ratio of the mass compared to the volume of a substance. A substance that is more dense has a greater mass for a specific volume. A substance that is less dense has less mass in the same volume. If you have a box that is one meter by one meter and fill it with helium (He) is will have less mass than if you fill the box with lead (Pb). Lead is denser than helium. If you want to do the math, Density (ρ) = mass / Volume.

Pressure: First, pressure is a force a substance feels when other substances push on it. If someone shakes your hand, you feel the pressure as they grip your hand. Scientifically, pressure is a term used when you talk about gases more than most states of matter. In physics, pressure is a ratio that measures a force over a specific area. In math, Pressure = Force / Area.

Vapor: Vapor is a type of gas. Vapor is not a pure gas like helium (H) or oxygen (O). Vapor exists at a temperature where you might also find liquid or solid versions of the same substance. You will find water vapor all over your daily life. Water vapor creates humidity and you might find water vapor coming out of a boiling teapot. Water vapor can easily condense back into a liquid if the temperature or pressure shifts.

Phase Diagram: A phase diagram shows the special points where a substance can go through a phase change. It usually has two axes that show temperature and pressure. Others show relationships between temperature and energy added to the system. For example, a phase diagram for water (at normal pressure) would have special points at 0-degrees Celsius when water freezes and 100-degrees Celsius when water boils.

Reference Materials

Wikibooks.org: http://en.wikibooks.org/wiki/General_Chemistry/Phase_Changes
Univ. of Colorado: http://phet.colorado.edu/en/simulation/states-of-matter
UC Davis: http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/ Phases_of_Matter/Phase_Transitions/Phase_Transitions
Wikipedia: http://en.wikipedia.org/wiki/Phase_transition


 
RELATED LINKS
- Chem4Kids: More Phase Changes
- Biology4Kids: Scientific Method
- Physics4Kids: Heat Expansion
- Geography4Kids: Earth Structure
- Geography4Kids: Hydrosphere
- Geography4Kids: Atmosphere
- Cosmos4Kids: Vacuum of Space

  RETURN TO TOP
or
Search for more information...

* The custom search only looks at Rader's sites.
 



Help Page Go for site help or a list of chemistry topics at the site map!
©copyright 1997-2014 Andrew Rader Studios, All rights reserved.
Current Page: Chem4Kids.com | Matter | Changing States of Matter


** Andrew Rader Studios does not monitor or review the content available at these web sites. They are paid advertisements and neither partners nor recommended web sites.