Dec 052011
 

Question by Restricted: What conversion factors needed to complete stoichiometry conversions?
What conversion factors needed to complete stoichiometry conversions?

Best answer:

Answer by Lucas C
Well it really depends on what you’re given to start with and what you’re asked to calculate.

The simplest stoichiometry problems are mole-to-mole conversions, and for those you need only a balanced chemical equation. The coefficients in the balanced equation are used to construct a conversion factor between moles of one substance and moles of a different substance in the same reaction.

If the problem involves mass, then you’re going to need to figure out the molar masses of one or both substances. For example, if the problem asks you to convert from grams of substance A to moles of substance B, you’ll need the molar mass of substance A. If you’re asked to convert from moles of substance A to grams of substance B, you’ll need the molar mass of substance B. If you’re asked to change from grams of substance A to grams of substance B (the most practical and common type of stoichiometric conversion) then you’re going to need the molar masses of both substances A and B.

That covers most stoichiometric conversions, but there there could be others. If you’re meant to convert to or from particles (meaning atoms, molecules, or ions) then you’ll have to use Avogadro’s number, 6.022×10^23, as a conversion factor. If your problem involves liters of a gas at STP, then you’ll have to know that at STP, 1 mole of any gas occupies a volume of 22.4 Liters. If you’re being asked to do stoichiometric conversions involving solutions, you’ll have to know the molar concentration of any solutions that are involved.

The key to working stoichiometry problems is to carefully analyze what you’ve got and where you need to go, then planning your steps carefully and executing them in strict order. Once you’ve got the basics, you can do any kind of stoichiometric conversion imaginable.

I hope that helps. Good luck!

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