# Chemical Forums

## Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: bw08f on February 13, 2009, 02:36:39 PM

Title: problem with general chemistry!!!! ahhh!
Post by: bw08f on February 13, 2009, 02:36:39 PM
I have no clue where to start or how to do this, any help will be appreciated:

1. you combine 10.0 g of hydrogen gas and 15.0 g of oxygen gas. how many grams of water vapor are made? which, if any, is your limiting reagent?
2H+O2->2H2O

2. magnesium metal will burn in the presence of oxygen gas forming mangesium oxide.
a. what is the balanced equation for this reaction?
b. how many grams of oxygen gas react with 20.0g of magnesium metal?
c. how many grams of magnesium oxide are made when 35.0 g of magnesium metal is burned in excess oxygen gas?

3. if 2.35 moles of H2 gas react with 5.33 mol of N2 gas to make amonia gas (NH3):
a. how many grams of NH3 can you make?
b. will there be any reactants left over? if so, which one and how many grams of it will remain?

thank you so much again!!
Title: Re: problem with general chemistry!!!! ahhh!
Post by: Arkcon on February 13, 2009, 04:06:23 PM
Well, lets start with the first one.  Your reaction for hydrogen and oxygen combining to form water, it isn't balanced, and your chemical shorthand for hydrogen isn't correct.  Can you fix that?  What are the units, understood, for the chemical reaction?  Can you convert the units you're given, to the units you need?
Title: Re: problem with general chemistry!!!! ahhh!
Post by: bw08f on February 14, 2009, 05:46:01 PM
4H+O2 -> 2H2O   here is the balanced equation, but im not sure how to do the shorthand for hydrogen is, sorry.

the units are grams and im not sure what you mean by convert the units im given to the units I need, everything seems to be in grams for the first part.  but for the second part im not sure which numbers in grams I need to convert to moles.
Title: Re: problem with general chemistry!!!! ahhh!
Post by: ARGOS++ on February 14, 2009, 06:16:44 PM

Dear bw08f;

Your equation is balanced now, but what Arkcon noted is that you forgot that Hydrogen is also a diatomic molecule as Oxygen is.

Do you know how grams must be converted into moles?
If yes, then you can solve it as normal "Stoichiometry Problem".

So you may apply the recipe/scheme from the Topic "Stoichiometry Problem":
"Stoichiometry Problem (#23'025) (http://www.chemicalforums.com/index.php?topic=23025.0)"
Therein is also an Example Diagram: How to do a "Stoichiometry Problem".

The same recipe you may then use to solve your other problems.
Good Luck!
ARGOS++