Unit 6: Phase changes

Question 1

solid to liquid

Answer 1

Melting. Gains energy.

Question 2

liquid to gas

Answer 2

Vaporizing. Gains energy

Question 3

solid to gas

Answer 3

Sublimation. gains energy

Question 4

gas to solid

Answer 4

deposition. loses energy

Question 5

gas to liquid

Answer 5

condensation. loses energy

Question 6

liquid to solid

Answer 6

freezing. loses energy

Question 7

What happens to temperature during a phase change?

Answer 7

The temperature plateaus. It remains constant during the phase change.

Question 8

A liquid is heated until the temperature plateaus. What is happening?

Answer 8

The liquid is boiling. It has reached its boiling point.

Question 9

A gas is cooled until the temperature plateaus. What is happening?

Answer 9

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.

Question 10

A solid is heated until the temperature plateaus. What is happening?

Answer 10

The solid is melting. It has reached the melting point.

Question 11

A liquid is cooled until the temperature plateaus. What is happening?

Answer 11

The liquid is freezing. It has reached the freezing point.

Question 12

What is the relationship between the freezing point and the melting point?

Answer 12

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.

Question 13

Distillation

Answer 13

A process used to separate a liquid mixture. Heat the mixture and one liquid will boil off first, then the other liquid.

Question 14

Heating curve

Answer 14

A graph showing the warming and phase changes of a substance. The axis are temperature and time.

Question 15

Cooling curve

Answer 15

A graph showing the cooling and phase changes of a substance. The axis are temperature and time.

Question 16

What usually happens to density during a phase change? Why is water an exception?

Answer 16

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.

Question 17

When exposed to heat, some solids melt while others burn. Why?

Answer 17

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.

Question 18

You put a substance into the Bunsen burner and it neither melts nor burns. Why?

Answer 18

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.