Stoichiometry

• Avogadro Constant

  6.022 x 10^23
• Mole


  One mole of a substance is equal to 6.022 x 10^23 particles of that substance (such as atoms, molecules or ions); denoted by "n", unit symbol is "mol"
• Formula for converting betweeen moles and no. particles


  n = no. particles/6.022 x 10^23
• Subscripts represent the no. atoms of each element present in a molecule of a substance
• The law of conservation of mass

  Mass is neither created nor destroyed by chemical or nuclear reactions, radioactive decay or by physical transformations
• The coefficient of each substance in the equation indicates the ratio in which the substances react
• Stoichiometry 


  The relationship between the relative quantities of substances taking part in a reaction or forming a compound, typically a ratio of whole integers
• Formula for mass percent composition

  % mass = mass of element/mass of compound * 100
• Percentage composition by mass

  The percentage by mass of each of the different elements in the compound.
• Molar mass

  Mass (g) of 1 mole of a substance, equal to the relative atomic mass; denoted by "M", unit symbol is "gmol^-1"
• Formula for no. moles

  no. moles = mass/molar mass

  n (mol) = m (g)/M (gmol^-1)
• Empirical formula

  A chemical formula that shows the simplest, whole number ratio of elements in a compound
• Molecular formula

  A chemical formula that shows the number of different atoms present in a molecule
• Limiting reagent

  The reactant that is totally consumed when the chemical reaction is complete (reactant that is used up first)
• Stoichiometric ratio

  Where the mole ratios for reactant atoms or molecules present in a chemical equation are in the exact proportion for the reaction to occur with no reactant in excess
• Theoretical yield

  The amount (mass) of a product that is produced from the complete reaction of the limiting reagent
• Experimental yield

  The actual yield (mass) of a product obtained for a reaction conducted in the laboratory
• Formula for percentage yield

  percentage (%) yield = experimental yield/theoretical yield * 100
• Excess reagent

  Reactant that is in excess when reaction is complete (reactant that is left over)
• no. moles -> no. particles?

  multiply by 6.022 * 10^23

  
• no. particles -> no. moles?

  divide by 6.022 x 10^23

  
• How can the molecular formula be deduced from the empirical formula?


  Solve for x, then multiply it by subscripts in empirical formula

  
• Identification of the limiting reagent depends on the mole ratios in the balanced chemical equation for the reaction
• ratio => coefficients, molar mass => subscripts
• Relative atomic mass


  The mass in grams of the number of atoms of the element contained in 12.00g of carbon-12; denoted by "Ar", unit symbol is "gmol^-1"
• Relative formula mass


  The sum of atomic masses of each element present in the formula; denoted by "Mr", unit symbol is "gmol^-1"

  To calculate Mr, add up the relative atomic masses of all elements in the formula
• Formula for concentration 


  *used when given volume instead of mass

  *note: 1dm^3 = 1L