CHEM 1303 Exam 1 - Chapters 2 and 3

Units of Measurement

• Key metric/SI units include:
  • Volume: liter (L)
  • Length: meter (m)
  • Mass: kilogram (kg)
  • Temperature: kelvin (K)
  • Time: second (s)

Measured Numbers and Significant Figures

• Measured numbers are obtained through measurement; exact numbers result from counting or defined quantities.
• Significant figures indicate the precision of a number; rules for counting significant figures include:
  • Non-zero digits are always significant.
  • Leading zeros are not significant.
  • Captive zeros (between non-zero digits) are significant.
  • Trailing zeros in a decimal number are significant.

Significant Figures in Calculation

• The result of a calculation should reflect the least number of significant figures from the values used.
• Rounding rules:
  • If the digit after the last significant figure is less than 5, round down.
  • If it is 5 or more, round up.

Prefixes and Equalities

• Metric prefixes denote multiples or fractions of a unit, allowing conversion in scientific calculations. For example:
  • kilo- (k) = 10³
  • centi- (c) = 10⁻²

Writing Conversion Factors

• Conversion factors facilitate changing between units; examples include:
  • 1 inch = 2.54 cm
  • 1 liter = 1,000 mL

Problem Solving Using Unit Conversion

• Dimensional analysis utilizes conversion factors to change units systematically in calculations. Ensure units cancel appropriately for accurate results.

Density

• Density (D) is calculated as mass (m) divided by volume (V): D = m/V.
• Knowing the density allows for determination of mass or volume when either is unknown.

Classification of Matter

• Matter is categorized as:
  • Pure substances: elements (unique types of atoms) and compounds (combinations of elements).
  • Mixtures: can be homogeneous (uniform composition) or heterogeneous (distinct, separate components).

States and Properties of Matter

• States of matter include solid, liquid, and gas, each exhibiting unique properties.
• Chemical properties pertain to the ability of a substance to undergo a chemical change, while physical properties can be observed without changing the substance.

Temperature

• Temperature conversions can be done among Celsius, Fahrenheit, and Kelvin. Conversion formulas include:
  • °C to °F: F = (C × 9/5) + 32
  • °C to K: K = °C + 273.15

Energy

• Energy exists in two main forms: potential energy (stored energy) and kinetic energy (energy of motion).
• Conversion of energy units may be required, such as joules to calories.

Energy and Nutrition

• Nutritional energy is measured in kilocalories (kcal) or kilojoules (kJ); caloric content can be calculated based on food composition.

Specific Heat

• Specific heat refers to the amount of heat required to change a unit mass of a substance by one degree Celsius.
• Analyze heat loss or gain during processes like heating or cooling using specific heat values.

Changes of State

• Changes of state include:
  • Melting: solid to liquid
  • Freezing: liquid to solid
  • Vaporization: liquid to gas
  • Condensation: gas to liquid
  • Sublimation: solid to gas
  • Deposition: gas to solid
• Heating and cooling curves illustrate temperature changes during phase transitions without calculations involving heat of fusion or vaporization.