II. Breakingitdown

For this question, answer each step.

2. When 85.00 g of sulfur dioxide and 100.0 g of oxygen gas react according to the balanced equation below, what is the theoretical yield in grams of SO3? How many grams of excess reactant remain?

2SO2 +O2 2SO3 Step 1:

To begin, lets convert grams of both reactants to moles of SO3 independently.

Convert from grams to moles of SO2 using the molar mass, then use the stoichiometric

coefficients from the balanced reaction to convert moles of SO2 to moles of SO3.

g SO2 _____________________________________ = mol SO3

Do the same for O2; convert to moles of O2, then moles of SO3.

g O2 _________________ ________________ = mol SO3

Step 2:

Which is the limiting reactant? (That is, which reactant makes the least product?)

Take the least number of moles of SO3 from Step 1 (produced by completely consuming the limiting reactant) and convert to grams of SO3 using the molar mass. (Only one of the values calculated above will be used in the first box. Choose the appropriate one.) This result is the theoretical yield.

Remember to take care of significant figures.

mol SO3 ______________ = g SO3

Step 4:

The second part of the question asks, How much excess reactant remains?

Which is the excess reactant? (That is, the one not completely consumed, the one remaining,

the one that made the most product, the one that is not the limiting reactant.)

First, calculate how much of the excess reactant was used in the reaction. Take the moles of SO3 produced by the limiting reactant above and convert back to moles of excess reactant using the stoichiometric coefficients. Then use the molar mass of the reactant to convert to grams of reactant. For example, if the excess reactant is X, convert from moles of SO3 to moles of X, to grams of X.

mol SO3 ______________ ______________ = g

This value is the amount of reactant actually used in the reaction. Step 5:

The final step is to subtract the result of Step 4 from the original number of grams of the excess reactant. Dont forget about sig. figs.

g g = gexcess