Question

Can you walk me through how to do a stoichiometry problem step-by-step?

I understand all the underlying principles pretty well, but when I go to complete them I get easily confused. I believe seeing how someone else does it would be helpful.

Answer 1

The key is to convert everything to moles. and then back to moles.

Explanation:

Step 1 balance the chemical equation.

Step 2 find out how many moles there are of the given substance.
A. change the values to moles.
1. if given grams change by dividing grams by grams per mole of the given substance ( the grams per mole can be found by using the periodic table.
2. if given volume convert to volume at STP then divide by the molar volume of 22.4 liters per mole.
3. If given number of particles divide by avogardor's number `6.02 xx 10^23`
Step 3 . Use the coefficients in the balanced chemical formula to find the ratio of moles for the values given to the the moles for the substance asked for

2 `AlO_3 == 2 Al + 3 O_2`

If same you calculated 4.3 moles of `AlO_3` in step 2 and you want to find the moles of `O_2` use the ratio of 3/2

`4.3 xx 3/2` = moles `O_2`

Step 4 change the moles of the substance asked for to what ever value is asked for.
1. multiply the moles calculated by the molar mass of the substance. ( the molar mass can be found using the periodic table.)
2. multiply the moles calculated by the molar volume 22.4 liters and then use the gas laws to change to a ta temperature pressure condition. ( hopefully not necessary)
3. multiply the moles calculated by Avogardro's number `6.02 xx 10^23` to find the number of particles. ( atoms, molecules or ions)

In summary using these four steps you find moles of one substance. Then change from moles of one substance to moles of the second substance. and change moles of the second substance to whatever value is asked for ( grams, volume, # particles. ) Works every time.