Chapter 1 : 1.1-Changing States Of Matter

Molecules can move from one physical state to another and not change their basic structure. Oxygen (O2) as a gas has the same chemical properties as liquid oxygen. The liquid state is colder and denser, but the molecules (the basic parts) are still the same. Water (H2O) is another example. A water molecule is made up of two hydrogen (H) atoms and one oxygen (O) atom. It has the same molecular structure whether it is a gas, liquid, or solid. Although its physical state may change, its chemical state remains the same.

Changes of Phase

Water vapor turning to frost is an example of deposition

There are four states of matter in the universe: plasma, gas, liquid and solid. But matter on Earth exists mostly in three distinct phases: gas, liquid and solid. A phase is a distinctive form of a substance, and matter can change among the phases. It may take extreme temperature, pressure or energy, but all matter can be changed.

There are six distinct changes of phase which happens to different substances at different temperatures. The six changes are:

• Freezing: the substance changes from a liquid to a solid.
• Melting: the substance changes back from the solid to the liquid.
• Condensation: the substance changes from a gas to a liquid.
• Vaporization: the substance changes from a liquid to a gas.
• Sublimation: the substance changes directly from a solid to a gas without going through the liquid phase.
• Deposition: the substance changes directly from a gas to a solid without going through the liquid phase.

Examples of Phase Change

I'm sure you know what most of these phases look like. Freezing is when liquid water freezes into ice cubes. Melting is when those ice cubes melt. Condensation is when dew forms on grass in the morning. Vaporization is when water boils and turns into steam. Deposition is one you may not know, but this happens when water vapor goes directly to freezing, like when there is frost on a cold winter morning. An example of sublimation happens when dry ice turns directly into gas. Gas can also change into a plasma. In order to do this you have to add an enormous amount of energy to the gas in order to free up the electrons from the atoms.