Mole to Mole Conversions

2 Reactant A + Reactant B --> 2 Product C + Product D
  • In the reaction above, compounds A and B react to produce compounds C and D.  
  • The coefficients show us that 2 moles of compound A are needed to react completely with 1 mole of compound B.  When these ratios are followed, 2 moles of compound C and 1 mole of compound D are produced.
  • Mole ratios can be written to represent numerical relationships between any two compounds in a chemical reaction.  The following ratios can be written for the reaction above:
    • 2 mole A : 1 mole B
    • 2 mole A : 2 mole C
    • 2 mole A : 1 mole D
    • 1 mole B : 2 mole C
    • 1 mole B : 1 mole D
    • 2 mole C : 1 mole D
  • Mole ratios are conversion factors that can be used in dimensional analysis.  We can rewrite the ratios in a fraction form. 
    • 2 mole A : 1 mole B is the same as   2 mole A / 1 mole B   or    1 mole B / 2 mole A
  • Identify the given compound and unknown compound in a word problem,  and use those two compounds in your mole ratio. 
  • Begin dimensional analysis by writing the given compound and draw the dimensional analysis chart.  Insert the identified mole ratio as a fraction.  Place the portion of the ratio containing the given compound in the denominator to cancel.
Example:  2 H2 + O2 --> 2H2O  
If 3.1 moles of H2 are used in the reaction, how many moles of O2 are needed to react completely?
NOTE:  H2 is the given compound, and O2 is the unknown compound.  Therefore, we'll use the mole ratio between H2 and O2 in the balanced equation.