Limiting Reactant & Percent Yield Multi-Step Problems

For the reaction P4O10 + 6 H2O -> 4 H3PO4, which reactant is limiting when 3.0 mol P4O10 react with 9.0 mol H2O?

• H3PO4 is the limiting component

• Neither is limiting; both completely react

• H2O is limiting under these amounts

• P4O10 is limiting under these amounts

Using the same reaction, what is the theoretical moles of H3PO4 formed from 3.0 mol P4O10 and 9.0 mol H2O?

• 4.0 mol of phosphoric acid produced

• 2.0 mol of phosphoric acid produced

• 6.0 mol of phosphoric acid produced

• 3.0 mol of phosphoric acid produced

Given the theoretical yield from the previous question and an actual yield of 575 g H3PO4, what percent yield results? (Molar mass H3PO4 ≈ 98.0 g/mol)

• Percent yield is about 73 percent

• Percent yield is about 88 percent

• Percent yield is about 59 percent

• Percent yield is about 98 percent

Balance the reaction for magnesium nitride formation: __ Mg + __ N2 -> __ Mg3N2. What are the smallest whole-number coefficients?

• 3, 1, 1 as balanced coefficients

• 2, 1, 1 as balanced coefficients

• 6, 1, 2 as balanced coefficients

• 1, 1, 1 as balanced coefficients

In the balanced reaction for Mg3N2, if 85.0 g Mg react with 65.0 g N2, which is the limiting reactant? (Molar masses: Mg ≈ 24.3 g/mol, N2 ≈ 28.0 g/mol)

• Neither; reaction is exactly stoichiometric

• Product limits the reaction progress

• Nitrogen gas is the limiting reactant here

• Magnesium is the limiting reactant here

From the same data, what is the theoretical mass of Mg3N2 produced? (Molar mass Mg3N2 ≈ 100.9 g/mol)

• About 94 grams of Mg3N2 produced

• About 100 grams of Mg3N2 produced

• About 141 grams of Mg3N2 produced

• About 118 grams of Mg3N2 produced

If 225 g of Mg3N2 are actually obtained from that reaction, what is the percent yield?

• Approximately 75 percent yield occurs

• Approximately 190 percent yield occurs

• Approximately 120 percent yield occurs

• Approximately 92 percent yield occurs

Which statement correctly describes the concept of limiting reactant in a chemical reaction?

• It gets used up first and limits product

• It is present in greatest starting mass

• It determines reaction rate and kinetics

• It is regenerated after reaction completes

Which formula correctly defines percent yield?

• Product grams divided by reactant grams times 100

• Actual yield divided by theoretical yield times 100

• Theoretical yield divided by actual yield times 100

• Limiting moles divided by excess moles times 100

Which expression correctly defines percent yield in chemistry?

• moles of product divided by moles of reactant used

• limiting reactant mass divided by excess reactant mass

• theoretical yield divided by actual yield times 100

• actual yield divided by theoretical yield times 100