Question

Question #17e2e

Answer 1

You are to determine the number of molecules of `NH_3` .

One molecule of `NH_3` contains 3 atoms of Hydrogen.So to produce one mole of `NH_3` we require `3/2molH_2` The following equation also supports that

`N_2+3H_2->2NH_3`

So 1 mole `H_2` produces `2/3mol NH_3`
Hydrogen taken `=7.98xx10^-4g`

`=7.98xx10^-4gxx1/(2.016g/"mol")`

So no.of moles of `NH_3` produced
`=2/3xx7.98xx10^-4gxx1/(2.016g/"mol")`

So no.of molecules of `NH_3` produced
`=2/3xx7.98xx10^-4gxx1/(2.016g/"mol")xx6.023xx10^23"molecule"/"mol"`
`=15.9xx10^19`molecules

Answer 2

Here's what I got.

Explanation:

The problem wants you to find the number of molecules of ammonia, `"NH"_3`, not hydrogen gas, `"H"_2`.

Your calculation is set up to find the number of molecules of hydrogen gas present in the `7.98 * 10^(-4)"g"` sample.

`7.98 * 10^(-4)cancel("g H"_2) * (1cancel("mole H"_2))/(2.016cancel("g H"_2)) * (6.022 *10^23"molec H"_2)/(1cancel("mole H"_2))`

`= 2.38 * 10^20"molecules H"_2`

As you can see, you're missing a conversion factor to take you from molecules of hydrogen gas to molecules of ammonia.

This conversion factor comes from the balanced chemical equation that describes the synthesis of ammonia

`color(blue)(3)"H"_ (2 (g)) + "N"_ (2(g)) -> color(purple)(2)"NH"_ (3(g))`

Notice that you have `color(blue)(3)` molecules of hdyrogen gas reacting with `1` molecule of nitrogengas to produce `color(purple)(2)` molecules of ammonia.

You can thus say that if you start with `x` molecules of hydrogen gas, you can get to molecules of ammonia by using

`xcolor(white)(a)cancel("molecules H"_2) * (color(purple)(2)color(white)(a)"molecules NH"_3)/(color(blue)(3)cancel("molecules H"_2)) = (2/3x)" molecules NH"_3`

In your case, you will have

`2.38 * 10^(20)cancel("molec H"_2) * (color(purple)(2)color(white)(a)"molec NH"_3)/(color(blue)(3)cancel("molec H"_2)) = 1.59 * 10^(20)"molec NH"_3`

In fact, you don't need to find the number of molecules of hydrogen gas, all you need to do is use the aforementioned `color(blue)(3):color(purple)(2)` mole ratio.

Since a mole is simply a fixed number of molecules, you can say that

`7.98 * 10^(-4)cancel("g H"_2) * (1cancel("mole H"_2))/(2.016cancel("g H"_2)) * (color(purple)(2)cancel("moles NH"_3))/(color(blue)(3)cancel("moles H"_2)) * (6.022 *10^23"molec NH"_3)/(1cancel("mole NH"_3))`

`= 1.59 * 10^(20)"molec NH"_3`

So remember, don't jump in head-first, make sure you understand what the problem wants you to find first.

Once you have a clear understanding of what you have and waht you need to calculate, organize your conversion factors and plug in your values.