how do you do stoichiometry?

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  • 1 decade ago
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    It's hard to tell you how to do it without a specific problem because each problem is set up differently. But the basis idea is to have like values opposite one another. Example:

    5 mole HCl x 36g HCl

    *********** 1 mole HCl

    Notice how the moles of HCl are diagonal from one another so that the moles cancel out and you are left with the grams of HCl. Also notice that 36g is equal to 1 mole of HCl so the 1 mole goes under that value. This question may be: "How many grams of HCl are in 5 moles of HCl?" If you were given a reaction in equation form, and were only given the number of moles of a different substance from the one you were finding you would need to set up a mole ratio in between. Say you were given:

    NaCl + H20 => NaOH + HCl

    First balance the equation. (in this case it is already balanced)

    Maybe the question is "if there are 3 moles of NaCl, how many grams of HCl will be formed from the reaction?" You would set it up like this:

    3 moles NaCl x 1 mole HCl x 36g HCl

    ***************** 1 mole NaCl 1 mole HCl

    The first value is you given. Then you would compare the mole ratios in the balanced reaction (in this case 1:1). Then you would put your value you are looking for on the top at the end (g HCl). Remember that the diagonals should be the same values (moles HCl with moles Hcl, moles NaCl with moles NaCl and g of whatever with g whatever). Hopefully that helps. And that astericks (*) are just empty space so you can see what goes under what.

    Source(s): chem student
  • 1 decade ago

    this is a really vague question, all i can tell you without details in your question is to make sure your unit conversions are correct and appropriate for the problem, because the numbers are easy as long as you have the correct units

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