[vort3x]

I'm doing practice questions for gas laws... and here's a question I'm not sure how to do. I thought about converting the volumes into masses by using density, and proceeding with stiochiometry... but because this is a gas law question I'm assuming there's an easier way to go about it? Any help would be appreciated:

Nitrogen and hydrogen gases react to form ammonia gas as follows:
N_2(g)+3H_2(g) -> 2NH_3(g)

At a certain temperature and pressure, 1.2L of N₂ reacts with 3.6L of H₂. If all the N₂ and H₂ are consumed, what volume of NH₃ at the same temperature and pressure, will be produced?

[Astrokel]

Avogadro's law

[typhoon2028]

It has been awhile since I have done a problem like this.

You do not know the pressure, so I don't think you can get mass through the density.

However, the question tells you that all of the N2 and H2 are consumed forming NH3.  So, I believe you can add the initial volumes for ideal gasses:  1.2L + 3.6L = 4.8L.  
Now according to the the reaction:  1 mole N2 + 3 moles of H2 = 2 moles NH3.  4 moles reactants make 2 moles of product.

Pressure and Temperature stay the same.
The only variables are V and # moles (n)

PV = nRT
PV/nRT = 1

P1*V1/n1*R*T1  = P2*V2/n2*R*T2

Pressure, temperature, and gas law constant cancel.  Leaving:  V1/n1 = V2/n2

4.8/4 = V2/2

V2 = 2.4 L

[vort3x]

Thanks, I do understand... but I'm having a lot of trouble re-arranging the ideal gas equation to incorporate the gas laws.

For example, here's another question I'm trying:
If the pressure exerted by Ozone (O₃), in the stratosphere is 3.0x10^-3 atm and the temperature is 250K, how many ozone molecules are in a liter?

----

So,
p = 3.0x10^-3 atm
t = 250K
v = ?
n = ?

I have two unknowns, once again not exactly sure what I have to do to re-arrange pv = nRt to support it? I've read the textbook section about gas laws and relating the ideal gas equation to the gas laws but it's not being specific enough...

[Astrokel]

At a certain temperature and pressure, 1.2L of N2 reacts with 3.6L of H2. If all the N2 and H2 are consumed, what volume of NH3 at the same temperature and pressure, will be produced?

If you know Avogadro's law well enough, you can just apply it without using the gas law.

I have two unknowns, once again not exactly sure what I have to do to re-arrange pv = nRt to support it? I've read the textbook section about gas laws and relating the ideal gas equation to the gas laws but it's not being specific enough...

V = 1 L as the question mentioned. Also what equation does n(moles) links to number of molecules? Can you replace n by that equation such that you have only one unknown?

[vort3x]

Silly me, liters is given... just kind of overlooked that.

Okay, I re-arranged pv=nrt and found n = 1.4 x 10^-4 moles

So to find molecules, all I do is the following, right?:

1.4 x 10^-4 x 6.022x10²³  = 8.43 x 10¹⁹ molecules?

[Astrokel]

You're correct!