# Question #17e2e

##### 2 Answers

You are to determine the number of molecules of

One molecule of

#N_2+3H_2->2NH_3#

So 1 mole

Hydrogen taken

So no.of moles of

So no.of molecules of

#### Answer:

Here's what I got.

#### Explanation:

The problem wants you to find the number of molecules of **ammonia**, **not** hydrogen gas,

Your calculation is set up to find the number of molecules of hydrogen gas present in the

#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 **molecules** of hdyrogen gas reacting with **molecule** of nitrogengas to produce **molecules** of ammonia.

You can thus say that if you start with

#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 **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.