Q: If only 6.9 g of $$\mathrm{PCl}_3 is $$collected from the reaction in the previous question, what is the percent yield?

$$\frac{6.9}{7.4} \times 100\% = 93.2\%$$

Q: If the reaction in the previous question actually produced 8.2 g of water, what is the percent yield?

$$\frac{8.2}{18} \times 100\% = 45.6\%$$

Q: Which of the following is the correct formula for calculating percent yield?

$$\text{Percent yield} = \frac{\text{Actual yield}}{\text{Theoretical yield}} \times 100\%$$

Q: A reaction has a theoretical yield of 12.0 g and an actual yield of 9.0 g. What is the percent yield?

$$\frac{9.0}{12.0} \times 100\% = 75\%$$

Question 1

Which of the following best describes the limiting reagent in a chemical reaction?

Accepted Answer

The reactant that determines the maximum amount of product that can be formed.

Question 2

Given the reaction: $$2 \mathrm{SO}_2(g) + \mathrm{O}_2(g) \rightarrow 2 \mathrm{SO}_3(g)$$, if you start with 4.0 moles of $$\mathrm{SO}_2$$ and 2.0 moles of $$\mathrm{O}_2$$, which is the limiting reagent?

Accepted Answer

Both are present in stoichiometric amounts; no limiting reagent.

Question 3

Suppose you have 3.5 moles of $$\mathrm{C}_2\mathrm{H}_5\mathrm{OH}$$ and 10.0 moles of $$\mathrm{O}_2$$ for the reaction: $$\mathrm{C}_2\mathrm{H}_5\mathrm{OH}(\ell) + 3 \mathrm{O}_2(g) \rightarrow 2 \mathrm{CO}_2(g) + 3 \mathrm{H}_2\mathrm{O}(\ell). $$What is the limiting reagent?

Accepted Answer

$$\mathrm{O}_2$$

Question 4

Elemental phosphorus ($$\mathrm{P}_4$$, 123.88 g/mol) reacts with chlorine gas ($$\mathrm{Cl}_2$$, 70.90 g/mol) to produce phosphorus trichloride ($$\mathrm{PCl}_3$$, 137.2 g/mol). If you have 5.2 g of $$\mathrm{P}_4$$ and 5.7 g of $$\mathrm{Cl}_2$$, what is the balanced equation for this reaction?

Accepted Answer

$$\mathrm{P}_4 + 6 \mathrm{Cl}_2 \rightarrow 4 \mathrm{PCl}_3$$

Question 5

Using the reaction $$\mathrm{P}_4 + 6 \mathrm{Cl}_2 \rightarrow 4 \mathrm{PCl}_3$$, if you have 5.2 g of $$\mathrm{P}_4$$ and 5.7 g of $$\mathrm{Cl}_2$$, which is the limiting reagent?

Accepted Answer

$$\mathrm{Cl}_2$$

Question 6

How many grams of $$\mathrm{PCl}_3$$ can be theoretically produced from 5.2 g of $$\mathrm{P}_4$$ and 5.7 g of $$\mathrm{Cl}_2$$? ($$\mathrm{P}_4$$: 123.88 g/mol, $$\mathrm{Cl}_2$$: 70.90 g/mol, $$\mathrm{PCl}_3$$: 137.2 g/mol)

Accepted Answer

7.4 g

Question 7

If only 6.9 g of $$\mathrm{PCl}_3 is $$collected from the reaction in the previous question, what is the percent yield?

Accepted Answer

$$\frac{6.9}{7.4} 	imes 100\% = 93.2\%$$

Question 8

In the reaction $$\mathrm{CH}_4 + 2 \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + 2 \mathrm{H}_2\mathrm{O}$$, if you start with 16 g of $$\mathrm{O}_2$$ and 16 g of $$\mathrm{CH}_4$$, how many grams of water are produced? ($$\mathrm{O}_2$$: 32 g/mol, $$\mathrm{CH}_4$$: 16 g/mol, $$\mathrm{H}_2\mathrm{O}$$: 18 g/mol)

Accepted Answer

18 g

Question 9

If the reaction in the previous question actually produced 8.2 g of water, what is the percent yield?

Accepted Answer

$$\frac{8.2}{18} 	imes 100\% = 45.6\%$$

Question 10

After the reaction between 5.2 g of $$\mathrm{P}_4$$ and 5.7 g of $$\mathrm{Cl}_2 is $$complete, how many grams of the excess reagent remain? ($$\mathrm{P}_4$$: 123.88 g/mol, $$\mathrm{Cl}_2$$: 70.90 g/mol)

Accepted Answer

3.6 g $$\mathrm{P}_4$$

Question 11

Which of the following best explains why the limiting reagent determines the amount of product formed in a chemical reaction?

Accepted Answer

It is the reactant that is completely consumed, stopping the reaction.

Question 12

A student mixes 10.0 g of $$\mathrm{SO}_2 ($$molar mass = 64.07 g/mol) with 10.0 g of $$\mathrm{O}_2 ($$molar mass = 32.00 g/mol) for the reaction $$2 \mathrm{SO}_2 + \mathrm{O}_2 \rightarrow 2 \mathrm{SO}_3. $$What is the limiting reagent?

Accepted Answer

$$\mathrm{SO}_2$$

Question 13

In a real-world scenario, why is it important for industrial chemists to identify the limiting reagent before scaling up a reaction?

Accepted Answer

To maximize product yield and minimize waste of expensive reactants.

Question 14

Which of the following is the correct formula for calculating percent yield?

Accepted Answer

$$	ext{Percent yield} = \frac{	ext{Actual yield}}{	ext{Theoretical yield}} 	imes 100\%$$

Question 15

A reaction has a theoretical yield of 12.0 g and an actual yield of 9.0 g. What is the percent yield?

Accepted Answer

$$\frac{9.0}{12.0} 	imes 100\% = 75\%$$

Question 16

Which of the following statements about excess reagents is correct?

Accepted Answer

Excess reagents are not completely consumed in the reaction.

Question 17

A chemist wants to produce 100 g of $$\mathrm{H}_2\mathrm{O}$$ using the reaction $$2 \mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2 \mathrm{H}_2\mathrm{O}. $$What mass of $$\mathrm{O}_2 is $$required? ($$\mathrm{H}_2\mathrm{O}$$: 18 g/mol, $$\mathrm{O}_2$$: 32 g/mol)

Accepted Answer

44.4 g

Limiting Reagents, Theoretical Yield, and Percent Yield in Chemical Reactions

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