GENCHEM_PRELIM

• Chemistry is the study of matter and its interactions, including how chemical molecules form and interact to create complex structures
• Chemistry impacts various aspects of our lives, such as medicine, communication, transportation, infrastructure, food science, agriculture, and many other technical fields
• Science is the process of learning about the natural universe through observation, testing, and generating models to explain observations
• Chemistry is one branch of science, with overlaps with other fields like biology (biochemistry) and geology (geochemistry)
• Physical properties describe matter, such as boiling point, melting point, and color, while chemical properties describe how the chemical structure changes during a reaction
• A substance that cannot be broken down into simpler components is an element, while a compound can be broken down into simpler components and is composed of more than one element
• The Periodic Table of Elements organizes the known chemical elements, with about 118 elements identified in the universe
• Atoms are the smallest part of an element that maintains its identity, while molecules are the smallest part of a compound that maintains its identity
• Mixtures are composed of two or more substances, with heterogeneous mixtures visibly containing different components and homogeneous mixtures having a consistent composition throughout
• Mixtures are composed of two or more substances, with heterogeneous mixtures visibly containing different components and homogeneous mixtures having a consistent composition throughout
• States of matter include solids (definite shape and volume), liquids (definite volume but not shape), and gases (neither definite shape nor volume)
• Phase changes are physical processes where a substance transitions from one phase to another based on temperature or pressure changes
• The scientific method is an organized procedure for learning answers to questions, involving proposing a hypothesis, testing it through experiments, and refining it if necessary
• Scientific notation allows us to express very large and very small numbers using powers of 10
• 10^0 = 1, 10^1 = 10, 10^2 = 100, 10^3 = 1000, 10^4 = 10000, 10^5 = 100000
• Scientific notation for large numbers involves finding the coefficient between 1 and 10 and multiplying it by 10 raised to a certain power
• Scientific notation for small numbers involves finding the coefficient between 1 and 10 and multiplying it by 10 raised to a negative power
• Example of large number in scientific notation: 579,000,000,000 = 5.79 x 10^11
• Example of small number in scientific notation: 0.0000642 = 6.42 x 10^-5
• Mass is measured in kilograms in the International System of Units (SI)
• 1 kilogram is equal to 1000 grams
• Mass and weight are not the same; mass is the amount of matter in an object, weight is the force of gravity acting on an object
• Mass remains constant regardless of location, weight varies depending on the gravitational pull
• Length is measured in meters in the SI system
• The meter is defined as the length traveled by light in a vacuum during a time interval of a second
• Temperature is a measure of the average kinetic energy of particles in a material
• Heat is the transfer of thermal energy from a warmer object to a cooler object
• Temperature scales: Celsius is based on the freezing and boiling points of water, Kelvin is based on absolute zero where molecules stop moving
• Lord Kelvin developed the Kelvin temperature scale with absolute zero as the starting point
• Fahrenheit scale: freezing point of water is 32°F, boiling point is 212°F
• To convert between Fahrenheit and Celsius scales:

  • [°C] = ([°F] - 32) × 5/9
  • [°F] = [°C] × 9/5 + 32
• The Kelvin temperature scale has its zero at absolute zero (-273.15°C) and uses the same degree scale as the Celsius scale
• Mathematical relationship between Celsius and Kelvin scales: K = °C + 273.15
• Chemists use the term "mole" to represent a large number of atoms or molecules

  • 1 mole (mol) represents 6.022 × 10^23 things
  • Avogadro’s number is 6.022 × 10^23
• Derived SI Units:

  • Derived units are combinations of SI base units
  • Area is a derived unit: square centimeter (cm²)
  • Volume is a derived unit: cubic meter (m³) or liter (L)
• Energy:

  • Energy has a derived unit of kg·m²/s²
  • Joule (J) is the SI unit of energy
  • 4.184 J = 1 cal
• Density:

  • Density is mass divided by volume
  • Units of density: g/cm³, g/mL, kg/m³
  • Density of water is about 1.00 g/mL
• Significant Figures:

  • Significant figures are all the digits known with certainty and the first uncertain digit
  • Rules for significant figures:
  • Trailing zeros at the end of a number may or may not be significant
  • All non-zero digits are significant
  • Trapped zeroes between non-zero digits are significant
  • Leading zeros are not significant
  • Trailing zeroes are significant after a decimal
  • Scientific notation shows all numbers as significant
  • A decimal point at the end of a whole number indicates all values to the left of the decimal are significant
• Exact Numbers:

  • Exact numbers are not measured by scientific instruments
  • Examples of exact numbers: defined units, counted items
  • Exact numbers do not affect the number of significant figures in calculations
• Rules of Rounding:

  • In scientific rounding, use "Rounding to the Even"
  • Increase the final digit by one unit if the dropped digit is 6 or greater
  • Leave the final digit unchanged if the dropped digit is 4 or lower
  • If the dropped digit is exactly 5, round to the even number