Amount of Substance

• Relative atomic mass (Ar) is 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) is 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
• For ionic compounds, relative formula mass is used
• The mole is a unit of measurement for substances and always contains the same number of particles, known as the Avogadro Constant (L)
• The mole is important in calculations where concentration is in moldm^-3
• Under standard conditions, gases and volatile liquids follow certain trends:

  • Pressure is proportional to temperature
  • Volume is proportional to temperature
  • Pressure and volume are inversely proportional
• The ideal gas equation is used with variables in standard units: pV = nRT

  • p = pressure in Pascals
  • V = volume in m^3
  • T = temperature in Kelvin
  • n = moles
  • m = mass in grams
  • R is the ideal gas constant, equal to 8.31 JK^-1 mol^-1
• Empirical formula is the simplest whole number ratio of atoms of each element in a compound, found using molar ratios of each element
• Molecular formula is the true number of each atom in the molecule, determined using the Mr of the empirical formula and the true Mr of the molecule to find a multiplier value
• Chemical equations must be balanced before they can be used in calculations to ensure correct reacting ratios
• Chemical equations can be used to calculate reacting masses, percentage yield, and atom economy

  • Percentage Yield
  • Atom Economy
  • High atom economy in industrial processes means little or no waste product, making the process economically viable and beneficial for the environment