Intro to General Chemistry

What is Chemistry?

Chemistry is the scientific study of matter, its properties, and the changes it undergoes. The basic functional unit of matter is the atom.

• Matter: Anything that occupies space and has mass.

• Matter can be classified into three main types:

  • Element: The simplest type of matter, composed of one kind of atom.

  • Compound: Matter composed of two or more different elements that are chemically bonded together.

  • Mixture: Matter composed of elements and/or compounds that are physically mixed together.

• Pure Substance: Has a fixed composition (elements and compounds).

• Mixture: Has a variable composition (homogeneous or heterogeneous).

Examples:

• Gold bar: Element

• Ammonia (NH3): Compound

• Orange juice: Mixture

• Wine: Mixture

• Saline solution: Mixture

Homogeneous Mixture: Uniform composition throughout (e.g., black coffee, seawater).

Heterogeneous Mixture: Non-uniform composition (e.g., trail mix, fruit salad).

Physical and Chemical Changes

Physical Changes

Physical changes affect the form of a substance, but not its chemical composition.

• Examples: Melting, freezing, dissolving, tearing, boiling, condensing.

• Physical changes are often reversible.

Chemical Changes

Chemical changes result in the formation of new substances with different chemical properties.

• Examples: Burning, rusting, cooking, digestion, color change due to reaction.

• Chemical changes are often irreversible.

Reversible vs. Irreversible Changes

• Reversible Change: Can be undone (e.g., melting and re-solidifying chocolate, dissolving sugar in water).

• Irreversible Change: Cannot be undone (e.g., baking a cake, burning wood).

Chemical and Physical Properties

Chemical Properties

Chemical properties describe a substance's ability to undergo chemical changes and form new substances.

• Examples: Reactivity with oxygen, flammability, acidity, toxicity, radioactivity.

Physical Properties

Physical properties can be observed or measured without changing the substance's chemical identity.

• Examples: Color, density, melting point, boiling point, hardness, luster, state of matter.

Intensive vs. Extensive Properties

Intensive Properties

Intensive properties do not depend on the amount of substance present.

• Examples: Density, temperature, color, melting point, boiling point, luster.

Extensive Properties

Extensive properties depend on the amount of substance present.

• Examples: Mass, volume, length, total charge, energy.

Temperature and Measurement

Temperature vs. Heat

• Thermal Energy: The sum of kinetic and potential energies of all atoms in an object.

• Temperature: The average kinetic energy of particles in a substance.

• Heat: The flow of thermal energy from a hotter object to a cooler one.

Temperature Conversions

• Common units: Celsius (ºC), Fahrenheit (ºF), Kelvin (K)

• Conversion formulas:

Scientific Notation

Format and Use

Scientific notation expresses very large or small numbers in the form where and is an integer.

• Coefficient: The number (must be ≥ 1 and < 10).

• Base: Always 10.

• Exponent: Indicates how many places the decimal is moved.

Conversions

• Positive exponent: Move decimal to the right (number gets larger).

• Negative exponent: Move decimal to the left (number gets smaller).

SI Units and Metric Prefixes

SI Base Units

Metric Prefixes

Significant Figures

Rules for Counting Significant Figures

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant.

• Trailing zeros in a decimal number are significant.

• Trailing zeros in a whole number with a decimal point are significant.

• Trailing zeros in a whole number without a decimal point are not significant.

• All digits in the coefficient of scientific notation are significant.

• Exact numbers have an infinite number of significant figures.

Significant Figures in Calculations

• Multiplication/Division: The result should have as many significant figures as the value with the fewest significant figures.

• Addition/Subtraction: The result should have as many decimal places as the value with the fewest decimal places.

Conversion Factors and Dimensional Analysis

Conversion Factors

A conversion factor is a ratio that expresses how many of one unit are equal to another unit.

• Example:

• Used to convert between units of length, mass, volume, etc.

Dimensional Analysis

Dimensional analysis is a systematic approach to problem-solving that uses conversion factors to move from one unit to another.

• Start with the given amount.

• Multiply by conversion factors so that units cancel appropriately.

• Continue until the desired unit is reached.

Density

Definition and Formula

Density is the amount of mass per unit volume.

• For solids and liquids: units are g/cm3 or kg/L.

• For gases: units are g/L or kg/m3.

Formula:

Density of Geometric Objects

• Volume formulas for common shapes:

  • Cube:

  • Sphere:

  • Cylinder:

Density of Non-Geometric Objects: Water Displacement

Water displacement is used to determine the volume of irregularly shaped objects by measuring the change in water level when the object is submerged.

Additional info: This guide covers foundational concepts in general chemistry, including classification of matter, physical and chemical properties and changes, measurement, significant figures, SI units, metric prefixes, conversion factors, dimensional analysis, and density. These topics are essential for success in any introductory college chemistry course.