the mathematics of chemical equations stoichiometry
TRANSCRIPT
Stoichiometry
• I. Stoichiometry- study of quantitative, or measurable, relationships that exist in chemical formulas and chemical reactions.
• II. Balanced Equations- The coefficients in a balanced chemical reaction indicate the number of moles of each substance participating in the chemical reaction.– Ex: 2H2 + O2 2H2O– 2 moles of hydrogen + 1 mole of oxygen yields 2 moles
of water.
Mole-Mole problems• Using a balanced equation you can determine amounts of
reactants or products.– Ex: Nitrous oxide is produced by the decomposition of
ammonium nitrate.• NH4(NO3) N2O + 2H2O• How many moles of N2O are produced from 2.25 moles of
NH4NO3?
Moles of given Moles of unknown
Use molar ratio to convert
Stoichiometry problems
• All stoichiometry problems are solved using a balanced chemical equation
• By doing so, you verify the Law of Conservation of Mass.
Mass-Mass Problems
• How many g of Cu(NO3)2 will be produced from 128 g of AgNO3?
• Cu + 2 AgNO3 Cu(NO3)2 + 2Ag
Mass of given
Moles of given Moles of unknown
Mass of unknown
Use molar mass Use molar
ratio
Use molar mass
Mass-mole problems
• How many moles of CO2 are produced from 64.8 g CO2?
• 2C2H2 + 5O2 4CO2 + 2 H2O
Mass of given Moles of given
Moles of unknown
convertUse molar ratio
Mole-mass problems
• What mass of H2O can be produced from 5.42 moles of glucose?
• C6H12O6 + 6 O2 4CO2 + 2 H2O
Moles of given
Moles of unknown
Mass of unknown
Use molar ratio
Use molar mass
Mass-Volume problems
• Sodium azide is the compound found in air bags. In a collision a sensor sets off a spark causing the NaN3 to decompose explosively, producing solid sodium and nitrogen gas: 2 NaN3 2Na + 3N2
• Assume an air bag contains 125 g of NaN3, what volume of N2 is produced?
• (Flow chart on next slide)
Mass-volume problems
Mass ofgiven
Moles ofgiven
Moles ofunknown
Volume of Unknown gas
Use molar mass
Use molar ratio
Use molar volume
Volume-volume problems
What volume of hydrogen gas is needed to react with 17.3 L of nitrogen gas?
N2 + 3H2 2NH3
Volume ofgiven
Moles ofgiven Moles of unknown
Volume of Unknown
Use molar volume
Use molar ratio
Use Molar volume
Limiting Reactants
• The limiting reactant (LR) is completely used up in the reaction.
• The other reactants will be left over, or “in excess”• The quantity (amount) of products formed in a rxn
are always determined by the quantity of the limiting reactant
• To determine the LR you do mass-mass problems
Limiting Reactant
• Determine the LR:
• Cu + 2AgNO3 Cu(NO3)2 + 2AgMass of
given
Moles ofgiven
Moles of unknown
Mass ofunknown
Determine LR
Percent Yield
• Ratio of the expected yield/actual yield
• Expected yield – amt of product that should be produced according to the balanced chemical equation.
• Actual yield- amt of product actually produced in the reaction