Chemical Principles: States of Matter, Atomic Mass, and Stoichiometry Laws

Factors Determining Changes of State

The changes in the state of a body are determined by several factors:

• The rise or drop in temperature.
• The rise or drop in pressure.
• The vapor pressure of a body.
• The state of cohesion or molecular aggregation.
• The chemical composition of the substance.

Defining Distillation

Distillation is a physical process of separating two or more liquids based on their boiling points.

Separating Complex Mixtures

A mixture of multiple substances (e.g., 10 substances) can often be separated effectively by chromatography.

Definitions of Phase Changes

• Fusion: The physical change from a solid state to a liquid state, typically achieved by increasing temperature.
• Solidification: The change from a liquid state to a solid state, typically achieved by decreasing temperature or increasing pressure.
• Liquefaction: The change from a gaseous state to a liquid state by lowering the temperature and increasing pressure.
• Sublimation: The direct change from a solid state to a gaseous state, bypassing the liquid phase.
• Condensation: The change from a gaseous state to a liquid state by lowering the temperature and increasing pressure.

True or False Statements on Physical and Chemical Phenomena

Indicate whether the following statements are True (T) or False (F):

• The formation of a mixture is a physical phenomenon. (T)
• Gases exhibit very large expansion forces. (T)
• Sublimation is the change from liquid to solid. (F) (Sublimation is solid to gas.)
• A chemical combination changes the properties of the components involved. (T)

Basis for Atomic Mass Calculation

The element that serves as the basis for the calculation of atomic masses is Carbon (specifically Carbon-12).

Absolute vs. Relative Atomic Mass

Absolute Atomic Mass

This refers to the actual mass of a single atom, typically measured in grams or kilograms (absolute weight).

Relative Atomic Mass

This is a dimensionless quantity calculated relative to a standard reference element. Historically, hydrogen was used; however, modern calculations use Carbon-12. It represents an approximate weight relative to this standard.

Defining the Mole

The mole (mol) is the SI unit for the amount of substance. It is a unit much larger than a single atom or molecule, defined as the amount of substance that contains exactly 6.022 x 10²³ elementary entities (Avogadro's number).

Fundamental Laws of Chemistry

Law of Definite Proportions (Proust's Law)

Different samples of a pure compound always contain the same elements in the same proportions by mass.

Law of Multiple Proportions (Dalton's Law)

When two elements combine to form different compounds, if the mass of one element remains fixed, the masses of the other element combine in ratios of small whole numbers.

Law of Reciprocal Proportions (Richter's Law)

The weights according to which two elements combine with each other are the same as the weights by which they combine with a third element.

Law of Combining Volumes (Gay-Lussac's Law)

Under the same conditions of pressure and temperature, the volumes of gases involved in a chemical reaction are always related to one another in ratios of small whole numbers.