Amount of substance

• Amount of substance


  The name given when counting the number of particles in a substance
• Amount of substance


  Often seen in calculations using the letter / symbol n
• Units for amount of substance

  Moles / mol
• Avogadro constant, N


  The number of particles equivalent to the relative atomic, molecular or formula mass of a substance
• The value of N is 6.02 x 10^23 g mol^-1
• Mole


  The mass of a substance with the Avogadro constant number of particles
• Molar mass


  The mass of substance that contains the same number of fundamental units as exactly 12.00 g of carbon-12
• Molar gas volume


  The volume occupied by one mole of any gas, at room temperature and pressure
• The molar volume is equal to 24 dm^3
• One mole of any element is equal to the relative atomic mass of the element, in grams
• One mole of carbon contains 6.02 x 10^23 atoms of carbon with a mass of 12.0 g
• One mole of water contains 6.02 x 10^23 molecules of water with a mass of 18.0 g
• Molecular formula


  Shows the number and type of each atom in a molecule
• Empirical formula


  Shows the simplest whole number ratio of the elements present in one molecule of the compound
• Empirical formula is the simplest whole number ratio of the elements present in one molecule or formula unit of the compound
• Molecular formula


  Gives the exact numbers of atoms of each element present in the formula of the compound
• Water of crystallisation


  When some compounds can form crystals which have water as part of their structure
• Hydrated compound

  A compound that contains water of crystallisation
• Anhydrous compound

  A compound which doesn't contain water of crystallisation
• The conversion of anhydrous compounds to hydrated compounds is reversible by heating the hydrated salt
• Number of moles


  Mass of a substance / Molar mass
• Reacting masses


  The masses of reactants that exactly react with each other to prevent waste
• The balanced chemical equation shows the ratio of moles of all the reactants and products, also called the stoichiometry, of the equation
• Moles

  The amount of a substance, measured in mol
• Molar mass


  The mass of one mole of a substance, measured in g mol−1
• Formula unit


  The smallest repeating unit of a compound
• One mole of CaF2 contains one mole of CaF2 formula units, but one mole of Ca and two moles of F ions
• Calculating reacting masses


  Obtain the balanced chemical equation

  2. The balanced equation shows the ratio of moles of all the reactants and products, also called the stoichiometry

  3. Use the mass of the reactants, the molar mass of the reactants, and the balanced equation to calculate the mass of products formed
• Stoichiometry


  The ratio of moles of all the reactants and products in a balanced chemical equation
• The stoichiometry of a reaction can be found if the exact amounts of reactants and products formed are known
• Gas volumes can be used to deduce the stoichiometry of a reaction
• Concentrated solution


  A solution with a high concentration of solute
• Dilute solution


  A solution with a low concentration of solute
• Calculating mass of substance in solution

  Change mass in grams to moles

  2. Change cm3 to dm3

  3. Use the concentration equation: number of moles (mol) = concentration (mol dm−3) x volume (dm3)

  4. Multiply the moles of solute by its molar mass to get the mass
• Avogadro's hypothesis


  Equal volumes of gases contain the same number of molecules
• At room temperature (20°C) and pressure (1 atm), one mole of any gas has a volume of 24.0 dm3
• Kinetic theory of gases

  Describes the behavior of gases based on the motion and interactions of gas molecules
• Assumptions of kinetic theory of gases

  • Gas molecules are moving very fast and randomly

  Molecules hardly have any volume

  Gas molecules do not attract or repel each other (no intermolecular forces)

  No kinetic energy is lost when the gas molecules collide with each other (elastic collisions)

  The temperature of the gas is related to the average kinetic energy of the molecules
• Ideal gas


  A gas that follows the kinetic theory of gases exactly
• Real gas


  A gas that does not follow the kinetic theory of gases exactly, but may come very close