C3

• Mole

  In chemistry, the amount of a substance that contains an Avogadro number (6.02 x 10^23) of particles (atoms, molecules, ions or electrons)
• The Avogadro constant is 6.02 x 10^23
• Relative atomic mass (A) or relative formula mass (M)


  The mass of one mole of atoms or molecules of a substance, in grams
• Relative formula mass examples


  • 1 mole of atoms of magnesium (Mg) has a mass of 24.3 g
  • 1 mole of molecules of water (H2O) has a mass of 18.0 g
• During chemical reactions, the mass of the products is the same as the mass of the reactants (law of conservation of mass)
• Reactions where mass seems to increase


  One or more reactants is a gas found in air (e.g. oxygen) and all the products are solids, liquids or aqueous
• Reactions where mass seems to decrease


  One of the products is a gas and all the reactants are solids, liquids or aqueous
• Limiting reactant


  The reactant that is used up first in a reaction, limiting the amount of product formed
• The amount of product formed is directly proportional to the amount of limiting reactant
• Gas volumes


  At the same temperature and pressure, equal numbers of moles of any gas will occupy the same volume (24 dm^3 per mole at room temperature and pressure)
• Concentration


  The amount of a substance (e.g. mass or moles) in a certain volume of a solution
• Calculating concentration in terms of mass


  Concentration (g/dm^3) = mass of solute (g) / volume of solution (dm^3)
• Atom economy


  The percentage of reactants that form useful products in a reaction
• Calculating atom economy


  Atom economy = (relative formula mass of desired products / relative formula mass of all reactants) * 100
• Reactions with high atom economies


  • They are economically and environmentally advantageous as they use fewer raw materials and produce less waste
• Atom economy


  Measure of how efficiently the atoms in the reactants are converted into the desired product
• Reactions with low atom economies aren't usually profitable
• Reactions with low atom economies produce more waste than reactions with high atom economies
• Raw materials can be expensive to buy, and waste products can be expensive to remove and dispose of responsibly
• Best way around problems of low atom economy

  Find a use for the waste products rather than just throwing them away
• There's often more than one way to make the product you want, so you could find a reaction that has a similar atom economy, but gives useful by-products rather than useless ones
• Reactions with high atom economies


  • Use fewer raw materials than reactions with low atom economies
  • Produce less waste
• Many raw materials will run out eventually, so it makes sense to use them efficiently so they last as long as possible
• Reactions with a higher atom economy also produce less waste, which is better for the environment as waste chemicals are often harmful and can be difficult to dispose of in a way that minimises their harmful effects
• Sustainable


  Using up as little of the Earth's resources as you can and not putting loads of damaging chemicals into the environment - in other words not messing things up for the future
• High atom economy processes tend to be more sustainable than low atom economy processes
• Percentage yield


  Measure of the amount of product you'd expect to get from a reaction compared to the amount of product that's actually formed
• Theoretical yield


  Amount of product you would get if all the reactants formed the desired products, and none of the products were lost
• Yield


  Amount of product you actually get in a reaction
• Even though no atoms are made or destroyed in reactions, in real life, you never get a 100% yield
• Reasons why percentage yields are never 100%


  • Reaction is reversible
  • Product is lost when separated from reactants
  • Unexpected side-reactions happening
• Reversible reaction


  Reaction where the products can themselves react to produce the original reactants
• In a reversible reaction, the reactants will never be completely converted to products because the reaction goes both ways
• When filtering a liquid to remove solid particles, you nearly always lose a bit of liquid or a bit of solid
• Some material is always left behind when transferring from one container to another
• Side-reactions


  Unexpected reactions happening, where the reactants may react with gases in the air or impurities rather than reacting to form the desired product
• Unexpected side-reactions mean a lower yield
• Factors to consider when choosing a reaction for industrial use


  • Atom economy
  • Yield
  • Reaction rate
  • Equilibrium position
  • Usefulness of by-products
• Industrial reactions are carried out on a much bigger scale than lab experiments, so they're more expensive and produce more waste
• Reactions with higher atom economies generally make industrial processes cheaper and more sustainable to run