CA7Science



One Force to Bind Them

Part 3: Changes of State

(The Return of the Binding)

Temperature drives atoms apart. Electric forces keeps atoms together. Specifically, electric forces caused by particles inside of atoms keeps atoms together. Not all particles are electric, e.g. neutrons. However, some are, and if they are electric they will be either positive or negative. Inside the atom protons are positive and electrons are negative. Like electric charges repel and unlike electric chargers attract.

( like charges repel

(opposites attract

(non-electric charges do nothing electric

The atom as a whole is held together by electric forces. Negative electrons orbit the nucleus because they are attracted by the positive protons in the nucleus.

(electric forces keep the electrons orbiting the protons

Atoms can also attract other atoms. The protons of one atom can attract the electrons of another atom. This causes atoms to be bound to one another and form solids or liquids, with solid bonds being stronger then liquid bonds. This is a weak attraction that can easily by broken by heating the substance. There is no attraction (or very little attraction) between gas or plasma particles.

[pic](above) atoms can attract other atoms

The attraction between atoms is sometimes referred to as polar forces, Van der Waal forces, interatomic or intermolecular forces.

Background

When matter changes from one form to another, it is said that is changing state. Another word for state is phase. Elements or compounds move from one state to another due to an increase or decrease in energy (temperature or pressure.)

When elements and compounds change states of matter, it is known as a physical change because no new chemicals are formed as a result of the phase change. We will focus on changes of state between solids, liquids and gases.

What state or phase change does each image represent?

[pic] [pic]

[pic] [pic]

| Phase Change |Terms |Change In Energy |Examples |

| | | |-ice cream melting |

| |Melting | | |

| | | |-melting chocolate |

| |Liquefaction* | | |

| | | |-solder |

| | | |-making ice cream w/ rock salt & ice |

| |Freezing | | |

| | | |-cooling lava into rock |

| |Solidification* | | |

| |Evaporation | |-puddles disappearing off the sidewalk after a |

| | | |summer rain |

| |Vaporization* | | |

| | | |-boiling water in a tea kettle |

| |Boiling | | |

| | | |-cooling the air to liquefy oxygen |

| |Condensation | | |

| | | |-dew on the grass |

| |Liquefaction* | | |

| | | | |

| |Solidification* | |-frost forming on a window |

| | | | |

| |Crystallization | | |

| | | |-mothballs disappearing as gas |

| |Sublimation | | |

| | | |-dry ice on a countertop |

| |Vaporization* | | |

| | | |-“solid” air fresheners giving off an odor |

*solidification, vaporization and liquefaction can refer to more than one type of change

Which phase changes are opposites?

Note: The temperature at which a phase change occurs is an example of a physical property of a substance.

Boiling Point-

Freezing Point-

Melting Point-

Dew Point-

Have you ever noticed that many cooking products, such as cakes or muffins, have special cooking instructions for areas at high altitudes? Why?

Try It!

1. Determine the Solid, Liquid and Gas Temperatures for each substance. The first one has been done for you.

|Substance |Melting Point |Boiling |Solid Temp. |Liquid Temp. |Gas Temp. |

| | |Point | | | |

|Ethyl Alcohol |-117(C |78(C | | | |

| | | | | | |

|Oxygen |-218(C |-183(C | | | |

| | | | | | |

|Mercury |-39(C |357(C | | | |

| | | | | | |

|Aluminum |660(C |2647(C | | | |

| | | | | | |

|Water |0(C |100(C | | | |

| | | | | | |

2. Using what you know about States of Matter, can you explain what happened in the picture below?

3. Identify the phase changes associated with each of the arrows.

[pic]

1. The temperature at which a solid turns into a liquid is called its _______________ ________________.

2. The temperature at which a liquid turns into a solid is called its _________________ ____________________.

3. The temperature at which a liquid becomes a gas is called its _______________ ______________.

4. Using the following Figure, first identify the two “points” that are missing and then determine that phase each of the following would be based on the temperatures given.

[pic]

| |Melt Pt |Boil Pt |

|Oxygen |-218°C |-183°C |

|Aluminum |660°C |2647°C |

|Water |0°C |100°C |

Oxygen at 0°C _______________

Aluminum at 100°C _____________

Water at 80°C ________________

Oxygen at -200°C ____________

Aluminum at 700°C ____________

Water at 120°C ______________

Hot Wax Lab

BACKGROUND:

Paraffin is a type of wax made out of crude petroleum. It is made of alkane hydrocarbons (straight-chained carbons and hydrogen’s joined together by a single bond)

NOTE: It takes at least 15 carbon atoms in a chain to have solid paraffin.

Paraffin can be used to make candles, candies, and beauty products.

ACTIVITY/PURPOSE

To observe the changes of state in paraffin and discover some important physical properties of paraffin.

Property – characteristics of a substance that make it unique

Physical Properties – properties of a substance that can observed without altering the substance

PROCEDURE/DATA COLLECTION

Record the freezing point temperature of wax.

Temperature ___________

What property have you discovered about paraffin? (Think of the point at which it turned from a liquid to a solid)

FOR FURTHER THOUGHT:

a. The melting point and freezing points of a substance are the same temperature. How would you prove this for paraffin?

b. The freezing point of water is 0(C. What is water’s melting point? How can you prove it?

c. Why would the knowledge of melting points be important when manufacturing cookware?

-----------------------

SOLID

LIQUID

GAS

Melting Pt

Boiling Pt

Solid Liquid Gas

OBSERVATIONS of Wax:

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