BackMatter, Measurement, and Chemical Change: General Chemistry Study Notes
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Ch.1 - Introduction: Matter & Measurement
Classification of Matter
Matter is anything that occupies space and has mass. It can be classified based on its composition and properties.
Pure Substances: Matter with a fixed composition. Includes elements and compounds.
Mixtures: Matter composed of two or more substances physically combined. Can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).
Type | Description | Example |
|---|---|---|
Element | Single type of atom | Oxygen (O2) |
Compound | Two or more elements chemically bonded | Water (H2O) |
Homogeneous Mixture | Uniform composition | Salt water |
Heterogeneous Mixture | Non-uniform composition | Salad |
Example: Classify the following substances: Gatorade (homogeneous mixture), Crystalline sugar (pure substance), Lead wire (element), Salsa (heterogeneous mixture).
Physical and Chemical Changes
Changes in matter can be classified as physical or chemical.
Physical Change: Alters the physical state or appearance without changing composition. Examples: Melting, boiling, dissolving sugar in water.
Chemical Change: Alters the chemical composition, forming new substances. Examples: Burning, rusting, cooking an egg.
Reversible and Irreversible Changes
Physical and chemical changes can be reversible or irreversible.
Reversible Change: Can be undone, restoring the original substance. Example: Dissolving sugar in water.
Irreversible Change: Cannot be undone. Example: Burning wood.
Phase Change | Bond Forming | Bond Breaking |
|---|---|---|
Gas → Liquid → Solid | Bond Forming | Bond Breaking |
Solid → Liquid → Gas | Bond Breaking | Bond Forming |
Chemical Properties
Chemical properties describe how a substance reacts with other substances, resulting in a change in composition.
Examples: Reactivity with acids, flammability, oxidation.
Example: High reactivity with oxygen is a chemical property.
Physical Properties
Physical properties can be observed or measured without changing the substance's chemical identity.
Examples: Color, melting point, density, state of matter.
Example: Mercury is a silvery liquid at 25°C (physical property).
Intensive vs. Extensive Properties
Properties of matter are classified as intensive or extensive.
Intensive Properties: Independent of the amount of substance. Examples: Density, melting point, color.
Extensive Properties: Depend on the amount of substance. Examples: Mass, volume, length.
Property Type | Examples |
|---|---|
Intensive | Density, temperature, color |
Extensive | Mass, volume, length |
SI Units and Measurements
The International System of Units (SI) is used for scientific measurements. Seven base units are defined for physical quantities.
Physical Quantity | Name | Symbol |
|---|---|---|
Length | meter | m |
Mass | kilogram | kg |
Time | second | s |
Temperature | kelvin | K |
Amount of substance | mole | mol |
Electric current | ampere | A |
Luminous intensity | candela | cd |
Perimeter, Area, and Volume:
Perimeter:
Area:
Volume:
Metric Prefixes
Metric prefixes are used to express multiples or fractions of SI units.
Prefix | Symbol | Multiplier |
|---|---|---|
kilo | k | |
centi | c | |
milli | m | |
micro | μ | |
nano | n |
Example: Convert 654 kg to g:
Temperature and Temperature Conversion
Temperature measures the average kinetic energy of particles. Common units are Celsius (°C), Kelvin (K), and Fahrenheit (°F).
Conversion formulas:
Scientific Notation
Scientific notation expresses very large or small numbers in the form .
Coefficient: Number between 1 and 10.
Exponent: Power of 10.
Example:
Significant Figures
Significant figures are the digits in a measurement that are known with certainty plus one estimated digit.
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.
Example: 0.00364 has 3 significant figures.
Precision in Measurement
Precision refers to how close repeated measurements are to each other. When recording measurements, include all certain digits plus one uncertain digit.
Significant Figures in Calculations
Multiplication/Division: Result has the same number of significant figures as the measurement with the fewest significant figures.
Addition/Subtraction: Result has the same number of decimal places as the measurement with the fewest decimal places.
Example: (rounded to one decimal place)
Conversion Factors
Conversion factors are ratios used to express a quantity in different units.
Common conversion factors: 1 inch = 2.54 cm, 1 kg = 1000 g, 1 L = 1000 mL
Conversion | Factor |
|---|---|
Length | 1 in = 2.54 cm |
Mass | 1 kg = 1000 g |
Volume | 1 L = 1000 mL |
Dimensional Analysis
Dimensional analysis is a method for converting between units using conversion factors.
Set up the problem so that units cancel, leaving the desired unit.
Multiply by conversion factors as needed.
Example: To convert 32 inches to centimeters:
Density
Density is the amount of mass per unit volume.
Formula:
Units: g/cm3 for solids and liquids, g/L for gases
Example: If a metal has a mass of 21.4 g and a volume of 10.0 cm3, its density is .
Density of Geometric Objects
For regular shapes, volume can be calculated and used to determine density.
Cube:
Sphere:
Cylinder:
Density of Non-Geometric Objects: Water Displacement
Water displacement is used to measure the volume of irregularly shaped objects.
Volume displaced = Final water level - Initial water level
Example: If water rises from 200 mL to 265 mL, the object's volume is 65 mL.
Additional info: These notes cover foundational concepts in General Chemistry, including matter classification, physical and chemical changes, properties, SI units, measurement, scientific notation, significant figures, conversion factors, dimensional analysis, and density. All examples and tables are reconstructed and expanded for clarity and completeness.
