Matter: Properties, States, and Mixtures in Chemistry

Posted on Nov 27, 2024 in Chemistry

• Definition of Chemistry

Chemistry is the science of chemical phenomena and the internal structure of matter.

• Definition of Physics

Physics is the science of physical phenomena.

• Physical and Chemical Phenomena

Physical phenomena affect some properties of substances without transforming them into new ones. Chemical phenomena produce new substances with the disappearance of others.

• Definition of Matter

Matter is anything that has mass and occupies a volume.

• Definitions of Mass and Volume. SI Units of Measurement

Mass is the amount of matter in a body. Its SI unit of measurement is the kilogram (kg).

Volume is the portion of space occupied by a body. Its SI unit of measurement is the cubic meter (m³).

• General and Specific Properties of Matter. Examples

General properties are common to all bodies and do not serve to characterize them. Examples: mass, volume.

Specific properties are characteristics used to determine or identify a substance. Examples: density, melting point.

• Definition of Density. Units of Measurement

Density is defined as the amount of mass per unit volume:

d =

The SI unit is kg/m³; other units include g/cm³, kg/L, etc. Density is a specific property of each substance. Tables are available to look up densities of different substances.

• Properties of Substances According to Their State

Matter exists in three different states of aggregation:

Progressive State Changes

• Melting: The change from solid to liquid. The melting point is a characteristic property of a substance and can be used to identify it. Melting point varies with pressure; as pressure decreases, melting point also decreases.
• Vaporization: The change from liquid to gas. It occurs at any temperature at the free surface of a liquid (liquids evaporate at any temperature). However, increasing the temperature leads to boiling, where large bubbles (filled with vapor) form within the liquid and rise to the surface. The temperature at which a liquid boils is called its boiling point, which varies with pressure. As pressure decreases, boiling point also decreases.
• Sublimation: The direct transformation from solid to gas without passing through the liquid state. Like vaporization, it occurs at any temperature (which is why we can smell solids; small portions sublimate and reach our noses as vapor). Most substances require very low pressures for significant sublimation.

Regressive State Changes

• Solidification: The change from liquid to solid. Occurs at the same temperature as melting and varies with pressure.
• Condensation: The change from gas to liquid.
• Deposition (Reverse Sublimation): The direct change from gas to solid without passing through the liquid state.

• Two Forms of Vaporization

Evaporation: The change of a surface portion of a liquid to vapor at any temperature. Evaporation increases with larger surface area and higher temperature.

Boiling: Occurs when enough heat is applied to a liquid. The transition to vapor occurs throughout the liquid’s mass, not just at the surface.

• Change of State Point vs. Change of State Temperature

The change of state point is the temperature at which a substance changes state at 1 atmosphere of pressure and is a characteristic property.

The change of state temperature is the temperature at which a substance changes state, which can vary with pressure and is not a characteristic property.

For example, water has a melting point of 0°C, but its melting temperature can be lower at higher altitudes where pressure is lower.

• Molecular Kinetic Theory of Gases, Liquids, and Solids

Why is water liquid, iron solid, and oxygen gas at room temperature and 1 atm pressure? The answer lies in the internal structure of matter.

All matter consists of tiny particles called atoms, which can link to form molecules or ions. Some substances are made of atoms (e.g., metals), others of molecules (e.g., water, oxygen), and others of ions (e.g., table salt).

Cohesive forces hold together the particles of a substance and determine its state of aggregation and characteristics.

The molecular kinetic theory explains the behavior of gases and can be extended to liquids and solids. Developed by Clausius in 1857, it is based on these points:

Gases

• Gases are composed of tiny, widely dispersed particles. The particles’ volume is negligible compared to the gas’s volume.
• Particles move in straight lines randomly, colliding with each other and the container walls. Speed depends on temperature.
• Attractive and repulsive forces between particles are negligible, allowing free movement.

Solids

• Solids are composed of particles held together by strong attractive forces. These particles cannot move freely but vibrate around fixed positions. Adding energy increases vibration speed.

Liquids

• Attractive forces in liquids are weaker than in solids. Particles can move but maintain a fixed average distance.

• Differences Between Pure Substances and Mixtures

• Pure substances have fixed characteristic properties, while mixtures do not.
• During melting or boiling, the temperature of a pure substance remains constant, unlike in mixtures.
• Components of a pure substance are separated by chemical processes; components of a mixture are separated by physical processes.
• The proportions of substances in a mixture are not fixed, while pure substances have fixed proportions.
• Substances in a mixture retain their properties; substances in a compound do not.

• Separation of Homogeneous and Heterogeneous Mixtures

Common separation procedures:

• Centrifugation: Separates solids from liquids based on density differences.
• Filtration: Separates solids from liquids based on particle size.
• Decantation: Separates a solid from a liquid after centrifugation or two immiscible liquids using a separatory funnel.
• Chromatography: Separates mixture components based on their adherence to a material’s surface.
• Crystallization: Separates a dissolved solid from a liquid based on volatility differences or removes impurities from a solid.
• Distillation: Separates immiscible liquids or a dissolved solid from a liquid based on boiling point differences.

• Classification of Solutions by Concentration

Solutions can be:

Diluted: Small amount of solute relative to the maximum.

Concentrated: Significant amount of solute relative to the maximum.

Saturated: Maximum amount of solute dissolved.

• Calculating Solution Concentration

Ways to express concentration:

Percent concentration =

Molarity, molality, normality, etc.