Seventh Grade Science

 Solids can become liquids and liquids can become solids  Liquids can become gases and gases can become liquids  Solids can become gases

 Melting is the process by which a solid becomes a liquid  Melting point – is the lowest temperature at which a substance begins to melt

 As solids heat up, the particles gain energy and vibrate faster causing the particles to break loose and slide past one another becoming a liquid

 Freezing is the process by which a liquid becomes a solid  Freezing point – is the temperature at which a specific liquid becomes a solid  The substance’s freezing point is the same as the substance’s melting point where the substance could exist either as a solid or a liquid

 As a liquid’s temperature is lowered, the particles lose energy and move more slowly.  Eventually, the particles move so slowly that the attraction among them cause the liquid to become a solid

 What are the ways in which a solid can change state into a liquid or that a liquid can change into a solid?

 Evaporation is the process by which a liquid becomes a gas  Evaporation usually occurs at the surface of a liquid  The fastest moving particles at the surface of the liquid break away from the liquid and become gas particles

 As the temperature increases, the energy in the liquid increases and the movement of the particles increases allowing them to escape from the liquid and become a gas

 Boiling is another process by which a liquid becomes a gas  Boiling point – is the temperature at which the liquid becomes a gas  Substances have specific boiling points  Ex. Water boils at 100 ⁰C or 212⁰F

 What are the ways in which a liquid changes state into a gas? What happens to the particles during that phase change?

 As the temperature increases, the energy in the liquid increases and the movement of the particles increases allowing them to escape from the liquid and become a gas

 Sublimation is when a solid changes directly to a gas  Ex. Dry ice is frozen carbon dioxide that sublimates

 Condensation is the process by which a gas becomes a liquid

 When you cool a gas, the particles move more slowly and the attraction between the particles increases pulling the particles closer together forming a liquid

 How does sublimation differ from condensation?