TEAS 3.2 Physical Properties and Matter

What are physical properties?

Characteristics you can observe without changing what the substance actually is. The identity of the substance remains the same even when its state changes.

What are the two types of physical properties?

• Intensive properties (stay the same no matter how much you have, like density and boiling point)

• Extensive properties (change based on the amount present, like mass and volume).

Define mass.

The specific number of molecules present in a substance

the actual amount of matter.

Define volume.

The amount of space that molecules occupy.

Define density.

The ratio of mass to volume.

Equation for density

Mass ÷ Volume

Density is measured in

g/cm³

What is the metric unit of mass?

Gram

Is density an intensive or extensive property?

Intensive property - it stays the same regardless of sample size.

What is the density of liquid water?

1 g/cm³

Why does ice float in water?

Solid water (ice) is less dense than liquid water, so it floats. This is unusual because most substances are denser as solids than as liquids.

How can density be used practically?

it can be used to identify unknown substances.

Denser substances sink in less dense substances, and less dense substances float.

What is the Kinetic Molecular Theory?

A theory stating that all molecules are in constant motion (except at absolute zero), and the temperature of a substance is directly proportional to the average kinetic energy of its molecules.

At what temperature do molecules stop moving?

Absolute zero: 0 K or -273°C

What are the four states of matter?

• Solid

• liquid

• gas

• plasma

Describe the molecular arrangement and motion in solids.

Molecules are packed tightly in an orderly, fixed pattern. They have only vibrational motion (vibrate in place) but no translational motion (don't move from place to place). Solids have definite shape and definite volume.

Describe the molecular arrangement and motion in liquids.

Molecules are less organized than in solids and exhibit both vibrational and translational motion.

they have definite volume but no definite shape (conform to container shape). Generally non-compressible.

Describe the molecular arrangement and motion in gases.

Molecules are rapidly moving and spread far apart with maximum translational motion

they have no definite volume or shape and are highly compressible.

What happens when you add heat to a substance?

You give energy to its molecules, which overcomes the intermolecular forces (attractions between molecules) that hold them together. This increases molecular motion.

Does heat break bonds within molecules or forces between molecules?

Heat breaks the forces between molecules (intermolecular forces), not the bonds within individual molecules.

What two conditions determine the state of matter?

• Temperature (pushes molecules apart)

• pressure (packs molecules together).

What is the triple point?

The point on a phase diagram where all three states (solid, liquid, and gas) can exist simultaneously.

What is the critical point?

The point on a phase diagram above which liquid and gas can coexist.

Define melting.

The phase change from solid to liquid that requires adding heat. Heat energizes molecules, breaks forces holding them in fixed positions, and molecules gain translational motion.

What is the difference between boiling and evaporation?

Both convert liquid to gas,

but boiling occurs throughout the liquid while evaporation occurs at the surface.

Both require heat energy input.

Define sublimation.

The transition of a substance directly from solid to gas without passing through the liquid state. Requires heat energy input.

What is an example of sublimation?

Dry ice (solid CO₂) changing directly from solid to gas at room temperature.

Define condensation.

The phase change from gas to liquid that occurs when heat is removed. Removing heat slows molecular motion and molecules come closer together.

What is an example of condensation?

Water droplets forming on a cold glass.

Define freezing.

The phase change from liquid to solid that requires removing heat. Further heat removal locks molecules into fixed positions; molecules lose translational motion and retain only vibration.

Define deposition.

The direct conversion from gas to solid without passing through the liquid phase. It is the opposite of sublimation.

What is an example of deposition?

Frost forming on windows when water vapor directly becomes ice crystals in cold temperatures.

Which phase changes require adding heat (energy input)?

• Melting (solid to liquid)

• boiling/evaporation (liquid to gas)

• sublimation (solid to gas)

Which phase changes require removing heat (energy release)?

• Condensation (gas to liquid)

• freezing (liquid to solid)

• deposition (gas to solid)

If you have 100 grams of an unknown metal occupying 187 cm³ of space, how would you identify it?

Calculate density:

100 g ÷ 187 cm³ = 0.534 g/cm³.

This matches lithium's density, so the metal is lithium.

Do solids have definite volume and shape?

Yes, solids have both definite volume and definite shape.

Do liquids have definite volume and shape?

Liquids have definite volume but no definite shape (they conform to the container).

Do gases have definite volume and shape?

No, gases have no definite volume or shape.

Are gases compressible?

Yes, gases are highly compressible.

Are liquids and solids compressible?

No, liquids and solids are generally non-compressible.

What type of motion do solid molecules have?

Only vibrational motion - they vibrate in place but don't move from place to place.

What types of motion do liquid molecules have?

Both vibrational and translational motion.

How does temperature relate to molecular motion?

Higher temperature means faster molecular motion

the temperature of a substance directly relates to how fast its molecules are moving.