## Stoichiometry Tutorial Finding and Using Molar Ratios

Example:

### Chem 1215

 4 moles NH3 5 moles O2
 4 moles NH3 4 moles NO
 4 moles NH3 6 moles H2O
 5 moles O2 4 moles NO
 5 moles O2 6 moles H2O
 4 moles NO 6 moles H2O
##### 6 Li (s) + N2 (g) --> 2 Li3N (s)

 6 moles Li 1 mole N2
 1 mole N2 6 moles Li
OR

Using molar ratios in calculations:

1. ##### Write down the units you are looking for, including the formula of the compound, and an equals sign:
 mol Li3N =
1. ##### Write the number of moles you were given in the problem
 mol Li3N = 0.24 mol Li

1. ##### Put a multiplication sign after the number of moles and draw a line:
2.  mol Li3N = 0.24 mol Li x ____________
1. ##### Above and below the line, write the molar ratio. Since you want to get rid of the units you started with (in this case "mol Li), put the units "mol" and the formula of the compound you started with on the bottom. Put the units "mol" and the formula of the compound you're looking for on the top.
 mol Li3N = 0.24 mol Li x ___mol Li3N mol Li
1. ##### Use the coefficients from the balanced chemical equation to complete the molar ratio. Place the coefficient in front of the formula that you started with on the bottom and the coefficient in front of the formula that you are looking for on the top. 6 Li (s) + N2 (g) --> 2 Li3N (s)
 mol Li3N = 0.24 mol Li x 2 mol Li3N 6 mol Li
1. ##### Cancel out the units and do the math.
 mol Li3N = 0.24 mol Li x 2 mol Li3N = 0.080 mol Li3N 6 mol Li

Practice Problems:

Use the following equation to answer the questions below:

2 CH3OH (l) + 3 O2 (g) --> 2 CO2 (g) + 4 H2O (l)