Chapter 2 – Chemistry and Measurements

Units of Measurement

In chemistry, measurements are fundamental for describing quantities such as mass, volume, and temperature. Standard units ensure consistency and accuracy in scientific communication.

• SI Units: The International System of Units (SI) is the standard system used in science. Common SI units include the meter (m) for length, kilogram (kg) for mass, and second (s) for time.

• Metric System: A decimal-based system of measurement used worldwide in science. Prefixes such as kilo-, centi-, and milli- indicate multiples or fractions of base units.

• Example: 1 kilometer (km) = 1000 meters (m)

Scientific Notation

Scientific notation expresses very large or very small numbers in the form a × 10n, making calculations and data presentation more manageable.

• Format: , where 1 ≤ a < 10 and n is an integer.

• Example: 0.00045 =

Significant Figures

Significant figures (sig figs) indicate the precision of a measured quantity. The number of significant digits reflects the certainty in the measurement.

• Measured vs. Exact Numbers: Measured numbers have limited precision; exact numbers (like counted items or defined conversions) have infinite significant figures.

• Rounding: When performing calculations, round the result to the correct number of significant figures based on the operation.

• Example: 2.34 × 1.2 = 2.8 (rounded to two significant figures)

Conversion Factors

Conversion factors are ratios used to convert one unit to another without changing the value of the quantity.

• Setup: Multiply by a fraction equal to one, with the desired unit in the numerator.

• Example: To convert 5.0 cm to meters:

Density

Density is a physical property defined as mass per unit volume. It is useful for identifying substances and solving conversion problems.

• Formula:

• Units: Commonly expressed in g/mL or g/cm3

• Example: If a sample has a mass of 10.0 g and a volume of 2.0 mL, its density is

Chapter 3 – Matter and Energy

Classification of Matter

Matter is anything that has mass and occupies space. It can be classified based on its composition and properties.

• Pure Substances: Have a fixed composition. Can be elements (single type of atom) or compounds (two or more elements chemically combined).

• Mixtures: Physical combinations of two or more substances. Can be homogeneous (uniform composition, e.g., salt water) or heterogeneous (non-uniform, e.g., salad).

States of Matter

Matter exists in different physical forms called states: solid, liquid, and gas. Each state has distinct properties.

• Solid: Definite shape and volume; particles are closely packed and vibrate in place.

• Liquid: Definite volume but no definite shape; particles are close but can move past each other.

• Gas: No definite shape or volume; particles are far apart and move freely.

Physical vs. Chemical Properties

Properties of matter can be classified as physical or chemical.

• Physical Properties: Observed without changing the substance's identity (e.g., color, melting point, density).

• Chemical Properties: Describe a substance's ability to undergo chemical changes (e.g., flammability, reactivity).

Physical vs. Chemical Changes

Changes in matter can be physical or chemical.

• Physical Change: Alters the form or appearance but not the composition (e.g., melting, dissolving).

• Chemical Change: Produces new substances with different properties (e.g., rusting, combustion).

Temperature

Temperature measures the average kinetic energy of particles in a substance. It is commonly measured in degrees Celsius (°C), Kelvin (K), or Fahrenheit (°F).

• Conversion Formulas:

• Celsius to Kelvin:

• Celsius to Fahrenheit:

• Fahrenheit to Celsius:

Specific Heat

Specific heat is the amount of heat required to raise the temperature of 1 gram of a substance by 1°C.

• Formula:

• Where q = heat (J), m = mass (g), c = specific heat (J/g·°C), ΔT = change in temperature (°C)

• Example: How much heat is needed to raise 50.0 g of water by 10.0°C? (c = 4.18 J/g·°C)

Energy and Nutrition

Energy is measured in joules (J) or calories (cal). In nutrition, the Calorie (with a capital C) is used, where 1 Calorie = 1 kilocalorie (kcal) = 1000 calories.

• Conversions:

• 1 cal = 4.184 J

• 1 kcal = 1000 cal

• 1 Cal (nutritional) = 1 kcal = 4184 J

Summary Table: Classification of Matter

Summary Table: Common Metric Prefixes

Additional Resources

• Online quizzes and dynamic study modules for practice on scientific notation, significant figures, and unit conversions.

• Video lessons and study guides for exam preparation.