Question

When `0.121" moles of HCl"` reacts with `0.399" moles of NH"_3`, how much `"NH"_3` is consumed?

`NH_3+HCl rarr NH_4Cl`

Answer 1

`0.121" mole of NH"_3` is consumed.

Explanation:

When we do Dimensional Analysis (a.k.a. The Factor-Label Method), we start with the given information written as a fraction over 1:

`(0.121" moles of HCl")/1`

From the equation we observe that `1" mole of NH"_3` reacts with `1" mole of HCl"`, therefore we multiply by this conversion factor:

`(0.121" moles of HCl")/1(1" mole of NH"_3)/(1" mole of HCl")`

Please observe that the units, `"moles of HCl"`, cancel and we are left with the units, `"moles of NH"_3`:

`(0.121color(red)(cancel" moles of HCl"))/1(1" mole of NH"_3)/(1color(red)(cancel" mole of HCl"))`

Here is the expression with the cancelled units removed:

`(0.121)/1(1" mole of NH"_3)/(1) = 0.121" mole of NH"_3`