Unit B-Chapter 2-Lesson 1

How Does Matter Change State?

States of Matter

Matter exists in three states:

• Solid
• Liquid
• Gas

A solid has a definite shape and definite volume
Example: Ice

A liquid has a definite volume, but no definite shape
Example: Water

A gas has no definite shape or volume.  It will occupy the volume of whatever container it is in.
Example:  Steam

• In a solid, particles of matter are very close together and are held together by the attraction of the particles for one another.
• When a solid, such as ice, is heated, its particles move faster and farther apart.  When the substance reaches its melting point, the solid changes to a liquid.
• Eventually the particles gain enough energy to escape.  When the particles reach this point, the substance becomes a gas.
• All three states of matter exist on earth.

Melting and Boiling

• Although most substances normally exist on Earth in just one state, all materials can exist as solids, liquids, or gases.

Example:
On the surface of Venus, which is very hot, lead would be a liquid rather than a solid as it is on Earth.

• The state of a substance depends on its temperature and the amount of attraction between its particles.
• The temperature at which a substance changes from a solid to a liquid state is called its melting point. 
• Melting occurs because particles gain heat.
• When the particles in a liquid lose energy, they move more slowly. 
• If the substance is cool enough, the particles slow down to the point where the liquid becomes a solid.
• The temperature at which a liquid changes to a solid is called its freezing point.
• In pure substances, melting and freezing occur at the same temperature.

Boiling and Evaporation

• If a liquid is heated enough, all the particles in the liquid eventually will have enough energy to break free at the surface. (The liquid changes to gas)
• The temperature at which this occurs is called the boiling point.
• Different substance have different boiling points.
• A substance can change from liquid to a gas through evaporation.
• Evaporation is the change in state from a liquid to a gas at the surface of a liquid.
• Evaporation can occur at any temperature because some of the particles at the surface always have sufficient energy to escape.
• However, evaporation takes place more quickly in hotter liquids.
• The change of state from a gas to a liquid is called condensation.