Question #c5bf9

A mole ratio or molar ratio a fraction made up from the coefficients in a balanced equation.

For example, in the equation

#"6Li(s)" + "N"_2"(g)" → "2Li"_3"N(s)"#

We could have the following mole ratios:

#"6 mol Li"/("1 mol N"_2)#; #"6 mol Li"/("2 mol Li"_3"N")#; #("1 mol N"_2)/"6 mol Li"#; #("1 mol N"_2)/("2 mol Li"_3"N")#; #("2 mol Li"_3"N")/"6 mol Li"#; and #("2 mol Li"_3"N")/("1 mol N"_2)#

EXAMPLE 1:

What is the mole ratio between #"Li"# and #"N"_2# in the reaction?

#"6Li(s)" + "N"_2"(g)" → "2Li"_3"N(s)"#

Solution:

#"6 mol Li"/("1 mol N"_2)# or #("1 mol N"_2)/"6 mol Li"#

We pick the fraction that gives us the correct units in a problem.

EXAMPLE 2:

Use the above equation to determine the number of moles of #"Li"_3"N"# that can be prepared using 0.24 mol #"Li"#.

Solution

The mole ratio is either #"6 mol Li"/("2 mol Li"_3"N")# or #("2 mol Li"_3"N")/"6 mol Li"#.

We choose the one that makes the units cancel and gives the correct units for the answer — the second one.

#0.24 color(red)(cancel(color(black)("mol Li"))) × ("2 mol Li"_3"N")/(6 color(red)(cancel(color(black)("mol Li")))) = "0.080 mol Li"_3"N"#