Unit 6: Phase changes Flashcards
solid to liquid
Melting. Gains energy.
liquid to gas
Vaporizing. Gains energy
solid to gas
Sublimation. gains energy
gas to solid
deposition. loses energy
gas to liquid
condensation. loses energy
liquid to solid
freezing. loses energy
What happens to temperature during a phase change?
The temperature plateaus. It remains constant during the phase change.
A liquid is heated until the temperature plateaus. What is happening?
The liquid is boiling. It has reached its boiling point.
A gas is cooled until the temperature plateaus. What is happening?
The gas is condensing. This happens at the same temperature as the boiling point. Outdoors, other factors besides temperature apply (such as humidity), and this is called the dew point.
A solid is heated until the temperature plateaus. What is happening?
The solid is melting. It has reached the melting point.
A liquid is cooled until the temperature plateaus. What is happening?
The liquid is freezing. It has reached the freezing point.
What is the relationship between the freezing point and the melting point?
They are the same! Both are the temperature at which the phase change solid→liquid or liquid→sold happens.
A liquid has a freezing point. A solid has a melting point.
Distillation
A process used to separate a liquid mixture. Heat the mixture and one liquid will boil off first, then the other liquid.
Heating curve
A graph showing the warming and phase changes of a substance. The axis are temperature and time.
Cooling curve
A graph showing the cooling and phase changes of a substance. The axis are temperature and time.
What usually happens to density during a phase change? Why is water an exception?
Usually a substance gains energy and becomes less dense as the intermolecular forces are overcome and the solid melts to liquid which vaporizes to gas. A substance losing energy usually becomes more dense. Water is an exception because as water freezes, it actually becomes less dense.
When exposed to heat, some solids melt while others burn. Why?
Some substances are made of carbon and carbon burns to create carbon dioxide. These are often organic substances, which come from living things. Other substances might be inorganic and will not burn easily.
You put a substance into the Bunsen burner and it neither melts nor burns. Why?
The substance is probably inorganic and held together by ion-ion force (the strongest IMF), or it is a metal and is not hot enough to reach its melting point.
