Posted by kim on Tuesday, November 15, 2011 at 2:55pm.
It would help if you told us what was confusing you. You have two equations. Balance them.
2WS3 + 9O2 ==> 2WO3 + 6SO2
2WO3 ==> 2W + 3O2
Here is the procedure for working stoichiometry problems. This will work all of them for you so print this out and save it.
1. Convert grams starting material to moles. moles = grams/molar mass.
2. You have moles WS3. You want to convert that to moles W. Use the coefficients in the balanced equation. Use the first equation to convert to mole WO3 and the second to convert to moles W.
?moles WS3 x (2 moles WO3/2 moles WS3) x (2 moles W/2 moles WO3). All of this becomes ?moles WS3 x (2/2)(2/2) = ?moles W.
3. Now convert moles W to grams W.
grams W = moles W x atomic mass W.
(Note: most problems don't have a two step synthesis of the desired product and they use only one set of conversions from starting material to end product and you COULD have worked two problems here. The first one would convert from grams WS3 to grams WO3 and the second problem would convert from grams WO3 to grams W but it is easier to convert both at the same time and it saves a couple of steps.). Post your work if you get stuck or post for an explanation about any of the steps.
thank you I get it now