Question

Calculate how many moles of NH3 form when 3.55 moles of N2H4 completely react according to the equation: 3N2H4 (l) ---> 4NH3 (g) + N2 (g) ?

Answer 1

`4.73` `"mol NH"_3`

Explanation:

What we're doing here is calculating basic mole-mole relationships, something that you'll be doing quite a bit!

The steps to solving mole-mole problems like this are

• write the balanced chemical equation for the reaction (this is given)

• divide the number of moles of the given known substance (`3.55`) by that substance's coefficient in the chemical equation (`3`)

• multiply that number by the coefficient of the substance you're trying to find (`4`)

Using simple dimensional analysis, it looks like this:

`3.55cancel("mol N"_2"H"_4)(larr "given amount")((4"mol NH"_3("coefficient"))/(3cancel("mol N"_2"H"_4)("coefficient")))`

`= color(red)(4.73` `color(red)("mol NH"_3`

rounded to `3` significant figures, the amount given in the problem.

Thus, if the reaction goes to completion, `3.55` moles of `"N"_2"H"_4` will yield `color(red)(4.73` moles of `"NH"_3`.