Physical Properties and Change of Matter: Mass, Volume, Density, and States of Matter

Physical Properties and Change of Matter

Objectives

This section introduces the fundamental physical properties of matter and the changes it undergoes. Understanding these concepts is essential for analyzing chemical phenomena and predicting material behavior under various conditions.

• Describe relationships between mass, volume, and density.

• Explain the states of matter in terms of molecular motion.

• Explain physical changes between states of matter (e.g., melting, evaporation, sublimation).

Physical Properties of Matter

Mass, Volume, and Density

Physical properties refer to observable attributes of a substance that do not change its chemical identity. The most fundamental properties include mass, volume, and density.

• Mass: The amount of matter in a substance, typically measured in grams (g) or kilograms (kg).

• Volume: The amount of space a substance occupies, measured in liters (L), milliliters (mL), or cubic centimeters (cm3).

• Density: The ratio of mass to volume, which helps identify substances and predict their behavior in mixtures.

Formula for Density:

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Example: If a 100 g sample of a metal occupies 187 cm3, its density is $\frac{100\,\text{g}}{187\,\text{cm}^3} = 0.534\,\text{g/cm}^3$. This matches the density of lithium, so the sample can be identified as lithium.

States of Matter

Solid, Liquid, Gas, and Plasma

Matter exists in four primary states: solid, liquid, gas, and plasma. The state depends on temperature, pressure, and molecular motion.

• Solid: Molecules are tightly packed, vibrating in place. Solids have definite shape and volume.

• Liquid: Molecules are less tightly packed, able to move past each other. Liquids have definite volume but take the shape of their container.

• Gas: Molecules are far apart and move freely. Gases have neither definite shape nor volume and expand to fill their container.

• Plasma: Ionized gas with free electrons, found at extremely high temperatures (e.g., stars).

Kinetic Molecular Theory: Explains that molecular motion increases with temperature, causing changes in state.

Changes Between States of Matter

Physical Changes: Melting, Boiling, Sublimation, and More

Physical changes involve transitions between states of matter due to energy (heat) transfer, without altering chemical composition.

• Melting: Solid to liquid. Requires addition of heat.

• Boiling/Evaporation: Liquid to gas. Requires addition of heat.

• Condensation: Gas to liquid. Requires removal of heat.

• Freezing: Liquid to solid. Requires removal of heat.

• Sublimation: Solid to gas directly (e.g., dry ice).

• Deposition: Gas to solid directly (e.g., frost formation).

Example: Solid carbon dioxide (dry ice) sublimates directly from solid to gas at room temperature. Water vapor can deposit as frost on windows in cold conditions.

Summary Table: States of Matter and Their Properties

State	Shape	Volume	Molecular Arrangement	Example
Solid	Definite	Definite	Tightly packed, fixed positions	Ice
Liquid	Indefinite (container shape)	Definite	Close, but able to move past each other	Water
Gas	Indefinite	Indefinite	Far apart, move freely	Water vapor
Plasma	Indefinite	Indefinite	Ionized particles, very high energy	Stars

Additional info: Plasma is not commonly encountered in everyday chemistry but is important in astrophysics and high-energy physics.