# of atoms when combining elements

  • #1
603
6

Homework Statement



One liter of nitrogen combines with 3 L of hydrogen
to form 2 L of ammonia. If the molecules of nitrogen
and hydrogen have two atoms each, how many atoms of
hydrogen and nitrogen are in one molecule of ammonia?


Homework Equations



Chemical equations

The Attempt at a Solution



I didn't know where to start so I looked at the solution key and got this:

The number of liters tells us how many molecules of the original combine to form this number of molecules of the product. Using these numbers as multipliers in a chemical equation gives us

1N2 + 3H2 → 1Nx Hy

Making sure that we have the same number of atoms of each kind on each side, we get x = 1 and y = 3.

Can somebody explain to me what the hell just happened?
 

Answers and Replies

  • #2
265
0
Try asking in the "Other Science" homework forum. While most of us here are capable of helping, this is a chemistry, not physics question.

As for what happened:
What is the relation between number of molecules and volume, given constant pressure and temperature?
 
  • #3
Nugatory
Mentor
12,988
5,699
You have two liters of ammonia, not one. So something is wrong with the right-hand side of the reaction as you've written it. Fix that and it will make sense.
 
  • #4
603
6
Sorry, this question came from my physics HW so I posted it here.
Maybe a moderator can move it.

Even when I change it to 2L it makes no sense to me. I haven't taken chemistry since high school.
 
  • #5
265
0
There are the same number of nitrogen molecules in 1L of nitrogen as there are hydrogen molecules in 1L of hydrogen and ammonia molecules in 1L of ammonia.
A nitrogen molecule is composed of two nitrogen atoms and a hydrogen molecule is composed of two hydrogen atoms. An ammonia molecule is composed of (for you) an unknown number of nitrogen and hydrogen atoms. That's where x and y came from.
You know that 1 part nitrogen molecule and 3 parts hydrogen molecule becomes 2 parts ammonia molecule. So [itex]1\times 2[/itex] parts nitrogen atoms becomes [itex]2\times x[/itex] nitrogen atoms and [itex]3\times 2[/itex] parts hydrogen atoms becomes [itex]2\times y[/itex] hydrogen atoms.
 
  • #6
603
6
Aaaah I see! Much appreciated Sir!
 

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