chem 1

A law summarizes what is observed in nature without providing an explanation.
A theory explains the underlying principles or mechanisms behind the observations.
Historical context: Many scientific laws were formulated before understanding the particle behavior of matter.

Solid:
- Retains its shape (e.g., a cube of solid does not change shape when dropped into a container).
Liquid:
- Adopts the shape of its container while maintaining a constant volume (e.g., the surface of a liquid in a tilted container remains parallel to the ground).
Gas:
- Expands to fill its container completely, with molecules moving independently from each other.

Solid: Similar to people crowded in rush hour in Tokyo, where they are packed closely and cannot move easily.
Liquid: Similar to people in a crowded mall, where there's still some movement but they remain somewhat constrained.
Gas: Comparable to being in a national park, where individuals are far apart and can move freely, reflecting the expansive nature of gas molecules.

Solid to Liquid: Melting or Fusion (endothermic process requiring heat absorption).
Liquid to Gas: Vaporization or Evaporation (endothermic).
Gas to Liquid: Condensation (exothermic process requiring energy release).
Liquid to Solid: Freezing (exothermic).
Solid to Gas: Sublimation (e.g., dry ice, sublimates directly without becoming liquid).
Gas to Solid: Deposition (e.g., formation of lab-grown diamonds).

Endothermic: Absorbs heat—transitioning from solid to liquid or from liquid to gas.
Exothermic: Releases heat—transitioning from gas to liquid or gas to solid.

Matter: Defined as anything that occupies space and has mass.
Pure Substances: Composed of one kind of matter with a constant composition.
Mixtures: Composed of two or more substances—can be homogenous (uniform appearance) or heterogenous (distinct, visible components).
Homogenous Mixture: E.g., saltwater where components cannot be visually distinguished.
Heterogenous Mixture: E.g., salad or concrete, where different components can be identified visually.

Elements: Simplest pure substances consisting of only one type of atom.
Compounds: Results from chemical bonding between two or more different atoms and can be separated chemically.

Intensive Properties: Independent of the amount of substance (e.g., density).
Extensive Properties: Dependent on the amount of substance (e.g., mass, volume).

Physical Properties: Can be observed without changing the substance's chemical composition (e.g. melting point, boiling point).
Chemical Properties: Involve a substance's ability to form new substances (e.g. reactivity, flammability).

Physical Change: Does not alter the chemical identity of the substance (e.g., melting, freezing).
Chemical Change: Changes the identity of the substance, forming new products (e.g., rusting of iron, cooking food).

Physical Changes: May involve alterations in appearance but do not produce new substances.
Chemical Changes: Often observable through factors like color change, gas formation, or temperature shifts.

Law of Constant Composition: A given compound always contains the exact same proportion of elements by mass.
Law of Definite Proportions: Compounds form in whole number ratios and cannot be fractions.
Law of Multiple Proportions: Different compounds may be composed of the same elements in different ratios, resulting in distinct properties.

Filtration: Separates particles based on size differences (e.g., straining pasta).
Distillation: Utilizes differences in boiling points to separate substances (e.g., saltwater).
Chromatography: Separates substances based on differences in solubility within a medium.
Centrifugation: Utilizes centrifugal force to separate substances based on density differences.

Law of Conservation of Mass: Mass remains constant in a closed system during physical or chemical changes.
Law of Conservation of Energy: Energy is neither created nor destroyed; it transforms and conserves in chemical and physical processes.
Energy can change forms (e.g., potential to kinetic) while total energy is conserved.

Understanding these fundamental concepts and properties helps in categorizing different forms of matter and recognizing the principles governing their interactions.