Amount of substance

• Relative atomic mass (Ar)


  The mean mass of an atom of an element, divided by one twelfth of the mean mass of an atom of the carbon-12 isotope
• Relative molecular mass (Mr)


  The mean mass of a molecule of a compound, divided by one twelfth of the mean mass of an atom of the carbon-12 isotope
• Relative formula mass


  For ionic compounds
• Mole


  A unit of measurement for substances that always contains the same number of particles
• Avogadro Constant (L)


  The number of particles present in a sample of a substance with known mass
• The mole is a very important unit of measurement in many calculations
• Ideal gas


  • Pressure is proportional to temperature
  • Volume is proportional to temperature
  • Pressure and volume are inversely proportional

  
• Standard units for ideal gas equation

  p = pressure in Pascals

  V = volume in m3

  T = temperature in Kelvin

  n = moles

  m = mass in grams

  
• Ideal gas constant (R)

  8.31 JK-1mol-1
• Empirical formula


  The simplest whole number ratio of atoms of each element in a compound
• Finding empirical formula


  Use molar ratios of each element

  
• Molecular formula


  The true number of each atom in the molecule
• Finding molecular formula


  Use Mr of empirical formula and true Mr of molecule to find a multiplier value to scale up the empirical formula
• Chemical equations must be balanced before they can be used in calculations
• Atom Economy


  The percentage of reactant atoms that end up in the desired product
• High atom economy is desirable in industrial chemical processes as it means little or no waste product, is more economically viable, and is more environmentally friendly