Question

If 4.88 grams of Zn reacts with 5.03 grams of S8 to produce 6.02 grams of ZnS, what are the theoretical yield and percent yield of this reaction? Be sure to show the work that you did to solve this problem.

unbalanced equation: Zn + S8 yields ZnS

Answer 1

I dont understand this?? can someone help??

Answer 2

So first you have to balance the equation,
\[8Zn _{(s)}+ S _{8(s)} \rightarrow 8ZnS_{(s)}\] Now you know that it takes 8 atoms of zn and that much sulfur to make that many molecules of zinc sulfide. The next step is to figure our the limiting reactant. The limiting reactant is the reactant that will be completely used up in the reaction. This reactant will dictate how much of product is formed and how much of the other reactant remains. The reason that the limiting reactant is is all used up has to do with the ratios of the molecular equation. The reactants chemically combine in the ratio use see in the equation. So for this reaction, the ratio will be 8Zn atoms per molecule of sulfur. If you have figure out with the given mass of chemicals,the ratio is say 2 zinc atoms per molecule of sulfur, then your limiting reactant is zinc because there are not zinc atoms to completely fulfill the ratio you see in the equation.

Answer 3

To figure out the limiting reactant, convert all the given masses of the reactants only to moles. The reason you do this is to figure out the ratios of the molecules between the reactants, you need to use moles as the number of atoms/molecules is counted in moles. Once you have all of the reactants converted from grams to moles, then you can figure out the ratio of the reactants to one another. So then you take the mol amount that is numerically greater and divide it by the mol amount that is numerically smaller.

Answer 4

This should give you the limiting reactant. Once you have the limiting reactant, go back and do a single calculation with dimensional analysis. In this calculation, you will use the mass of the limiting reactant, convert that mass to moles (I know you do it again), then you know the ratios of the chemicals, so you can figure out the moles of product that will be formed theoretically with that limiting reactant.

Answer 5

Convert that moles of product into grams using molar mass. This is your theoretical yield. It means that given the limiting reactant that you have, theoretically, this is how much product you can form. In real life however sometimes you may have less or more yield when you actually carry out this reaction with the given masses of reactants. The reason for this difference is that in real life, you may not easily collect all of the yield, or there may errors in measurement, or the equipment you are using to produce this reaction. Therefore, you must figure out the percent yield. The formula for percent yield is what you actually got over the theoretical yield. Once you have that decimal multiply by 100 and you have your percent yield.