Introduction to General Chemistry: Classification of Matter, Properties, and Measurement - Edited

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Intro to General Chemistry

Classification of Matter

Test Table

Example: Crystalline sugar is a pure substance; salsa is a heterogeneous mixture.

Physical and Chemical Changes

Changes in matter can be classified as physical or chemical:

Physical Change: Changes in the physical state or appearance of a substance without altering its chemical composition (e.g., dissolving sugar in water, melting ice).
Chemical Change: Changes in chemical composition that result in new substances with different properties (e.g., burning wood, rusting iron).

Example: Dissolving sugar in water is a physical change; burning wood is a chemical change.

Reversible and Irreversible Changes

Reversible changes can be undone (e.g., freezing and melting water), while irreversible changes cannot easily be reversed (e.g., burning paper).

Phase changes (solid <-> liquid <-> gas) are common reversible changes.
Chemical reactions are often irreversible.

Example: Dissolving sugar in water is reversible; burning wood is irreversible.

Chemical and Physical Properties

Chemical Property: A property observed during a chemical reaction (e.g., flammability, reactivity with acids).
Physical Property: A measurable property that describes the state of a chemical compound without changing its chemical structure (e.g., color, melting point, density).

Example: Mercury is a silvery liquid at 25°C (physical property); sodium reacts violently with water (chemical property).

Intensive vs. Extensive Properties

Intensive Properties: Do not depend on the amount of substance (e.g., density, boiling point, color).
Extensive Properties: Depend on the amount of substance (e.g., mass, volume, energy).

Example: Density is intensive; mass is extensive.

Mathematical Operations and Functions

Temperature and Thermal Energy

Thermal Energy: The sum of kinetic and potential energies of all atoms in an object.
Temperature: The average kinetic energy of atoms in a substance.

Temperature is measured in units of Celsius (°C), Kelvin (K), or Fahrenheit (°F).

Temperature Conversion Formulas:

Scientific Notation

Scientific notation expresses very large or small numbers in the form .
Coefficient: The number between 1 and 10.
Exponent: The power of 10.

Example:

SI Units and Metric Prefixes

The International System of Units (SI) is based on seven base units (meter, kilogram, second, ampere, kelvin, mole, candela).

Physical Quantity	Name	Symbol
Length	meter	m
Mass	kilogram	kg
Time	second	s
Temperature	kelvin	K
Amount of substance	mole	mol

Metric prefixes (e.g., kilo-, centi-, milli-) are used to express multiples or fractions of base units.

Significant Figures

Significant figures are the digits in a measurement that are known with certainty plus one estimated digit.
Rules for counting significant figures depend on the presence of zeros and decimal points.

Example: 0.00364 has 3 significant figures.

Precision in Measurements

When recording measurements, include all certain digits plus one uncertain digit.
Use the correct number of significant figures when reporting measurements.

Significant Figures in Calculations

For multiplication/division: The result should have the same number of significant figures as the value with the fewest significant figures.
For addition/subtraction: The result should have the same number of decimal places as the value with the fewest decimal places.

Conversion Factors and Dimensional Analysis

Conversion Factor: A ratio used to convert from one unit to another (e.g., 1 inch = 2.54 cm).
Dimensional Analysis: A method to solve problems by converting units using conversion factors.

Example: To convert 115 minutes to years, use the appropriate conversion factors to cancel units.

Density

Density is the amount of mass per unit volume.

Density Formula:

For solids and liquids, density is usually expressed in or ; for gases, in .

Density of Geometric and Non-Geometric Objects

For regular shapes, use geometric formulas to find volume (e.g., cube: ).
For irregular shapes, use water displacement to determine volume.

Example: If a cube of silver (density = 10.5 g/cm³) measures 3.60 cm on each side, its mass is .

Water Displacement

Water displacement is used to measure the volume of irregularly shaped objects by noting the change in water level.

Example: If the water level rises from 200 mL to 265 mL after submerging an object, the object's volume is 65 mL.

Additional info: These notes cover foundational concepts in general chemistry, including the classification of matter, properties, measurement, and basic mathematical operations essential for laboratory and theoretical work.