Amount of substance

• What is the definition of 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.
• What is the definition of 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.
• What does the Avogadro Constant (L) represent?


  The number of particles in one mole of a substance.
• How can the number of particles in a sample of a substance be found?


  By using the Avogadro Constant (L) with the known mass of the substance.
• What is the formula for calculating concentration in moles?


  Concentration = n / V, where n is moles and V is volume in $m^3$.
• What is the ideal gas equation?


  PV = nRT, where P is pressure, V is volume, n is moles, R is the ideal gas constant, and T is temperature.
• What are the standard units for pressure, volume, temperature, and mass in the ideal gas equation?

  Pressure in Pascals, volume in $m^3$, temperature in Kelvin, and mass in grams.
• What is an empirical formula?


  The simplest whole number ratio of atoms of each element in a compound.
• Why must chemical equations be balanced before calculations?


  To ensure the reacting ratios are correct.
• What can balanced chemical equations be used to calculate?


  Reacting masses, percentage yield, and atom economy.
• What does a high atom economy indicate in industrial chemical processes?


  There is little or no waste product, making the process more economically viable.
• Why is high atom economy beneficial for the environment?


  It uses less natural resources and often requires less energy.