[JonathanEyoon]

Water can be formed from the stoichiometric reaction of hydrogen with oxygen:



A complete reaction of 5.0 g of O2 with excess hydrogen produces how many grams of H2O?



I'm having a worst time with this one than the other one I had.  I don't even know where to start off  Any help is much appreciated.

[ARGOS++]

Dear JonathanEyoon;

“Every” Stoichiometry Problem starts with the same Steps:

• A.)   Build the “Reaction Equation” for your Problem.
• B.)   Balance¹⁾ the “Reaction Equation” with the required Indices, giving you the Stoichiometry. 
• C.)   Translate the known masses for the “Reaction Equation” into the corresponding number of Moles.
• D.)   Maybe you have to find the limiting Reagent.
• E.)   Calculate from C.) and D.) the still missing masses using the number of Moles from the “Reaction Equation”. 
• F.)   Identify your Result.

¹⁾ For “How to Balance a Chemical Reaction” you may read on: "Balancing Chemical Equations”
²⁾ How the ‘whole’ Diagram/Scheme for the second Example must look you can see on the:  "Replay #36 and #37”.

I hope this small Recipe may be of help to you to solve your Stoichiometry.

Good Luck!
                    ARGOS⁺⁺

[JonathanEyoon]

I don't even know how to set up the problem  That's why i'm having such a hard time with this stuff.

[Sev]

Start with rxn eqn (as Argos++ mentioned)

[JonathanEyoon]

ok. How do I start that?

[ARGOS++]

Dear JonathanEyoon;

Let’s try to do A.) and B.) together:

A.)         Reaction:        O₂   +     H₂    ----->    H₂O.
B.)         Balancing:     1O₂   +   2H₂    ----->  2H₂O. 
C.)         Are you able to find all required Molecular Weights (MW), and translate your 5.0 g O₂ into the Number of Moles?

Will this be enough for the Start?

Good Luck!
                    ARGOS⁺⁺

[JonathanEyoon]

yea I know how to find MW and convert to mols.  What do I do from there?

[Sev]

Use mole ratios - every mole of O₂ gives 2 mole of H₂O.

[ARGOS++]

Dear JonathanEyoon;

As C₁.)   Write below the Reaction Members the corresponding MWs, and
As C₂.)   Write the translated Moles of 5.0g O₂ below its MW.

For   D.) you know that the Amount of O₂ is the only limiting Reagent.
From E.) and B.) you know  how many moles water you can build from one Mole O₂, and so you can calculate the Amount  in Moles and Grams  of Water you have build.     


Good Luck!
                    ARGOS⁺⁺

[JonathanEyoon]

  i'm completely lost.  Is there any way you could do this one problem for me?  I want to see an example of how to do a problem of this kind.  I have 14 more after this one    Any help is much appreciated.

[Arkcon]

yea I know how to find MW and convert to mols.  What do I do from there?

Great.  You're given amounts in units of grams.  The balanced chemical equation is in units of moles.  You want the answer in grams. 

So convert grams of reactant to moles, use the balanced equation to convert moles of reactant into moles of product (hey, why do you think we call it a balanced equation?  It is a function that you've derived, just like mathematics, for the purpose of converting moles of product into moles of reactants.)  Then convert moles of product back into grams, for the answer.

[Arkcon]

i'm completely lost.  Is there any way you could do this one problem for me?  I want to see an example of how to do a problem of this kind.  I have 14 more after this one    Any help is much appreciated.

At least show us that you can determine molecular weight, and convert grams to moles, like you assured us you can.  Then try to follow the steps outlined by ARGOS++.  Sev's suggestion is good as well, but you may need a bit more expertise, before his suggestion becomes intuitive, and not confusing for you.

[ARGOS++]

Dear JonathanEyoon;

Don’t fear!

From the indices given on B.) you know that from 1 Mole O₂ you can build 2 Moles Water.
So Please tell me how many Moles of O₂ you have (= 5.0g), and how many Moles of Water you have built.


Good Luck!
                    ARGOS⁺⁺

[JonathanEyoon]

Wait, how do we get 2 H20's from 1 mole of 02?  Don't we need a hydrogen for that to happen?  5.0g of oxygen to mols should be

.3125 moles

How do you find how many moles of water i've built?

[ARGOS++]

Dear JonathanEyoon;

Sorry!,  ─   
I got 0.15625 Moles, because the MW of O₂ is 32.0 and not 16.0!
With an Excess of H₂ you can build 2 * 0.15625 Moles Water (from B.)).
How many Water will this now be?


Good Luck!
                    ARGOS⁺⁺