Q: Which formula correctly expresses percent yield?

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

Question 1

When balancing a chemical equation, what must be equal on both sides of the equation?

Accepted Answer

The number and type of atoms

Question 2

What is the sum of the coefficients when the following equation is balanced? $$\_\_\_\ Al_4C_3\ (s) + \_\_\_\ H_2O\ (l) \rightarrow \_\_\_\ Al_2O_3\ (s) + \_\_\_\ CH_4$\ (g)$$

Accepted Answer

14

Question 3

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

Accepted Answer

It is the reactant that is completely consumed and determines the maximum amount of product formed.

Question 4

Given the reaction: $$2\ H_2$\ (g) + O_2$\ (g) \rightarrow 2\ H_2O\ (g)$$, how many grams of $$H_2O$$ are produced from 12.3 g of $$H_2$$?

Accepted Answer

110.7 g

Question 5

A reaction between 12.0 g $$C_3H_6$$, 10.0 g $$NH_3$$, and 5.0 g $$O_2$$ produces acrylonitrile ($$C_3H_3N) $$according to: $$2\ C_3H_6 + 2\ NH_3$ + 3\ O_2$ \rightarrow 2\ C_3H_3N + 6\ H_2O. $$What is the mass of acrylonitrile produced, assuming 100% yield?

Accepted Answer

5.6 g

Question 6

Which formula correctly expresses percent yield?

Accepted Answer

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

Question 7

If a reaction has a theoretical yield of 10.0 g and an actual yield of 7.5 g, what is the percent yield?

Accepted Answer

75%

Question 8

In a laboratory, 22.1 g of Cu is isolated by reacting 45.5 g Zn with 70.1 g $$CuSO_4. $$What is the percent yield if the theoretical yield is 28.0 g?

Accepted Answer

78.9%

Question 9

Which of the following is NOT a step in solving a stoichiometry problem?

Accepted Answer

Balance the equation after calculations are complete

Question 10

A reaction produces 1.25 g of $$H_2O$$ from 2.6 g of $$C_6H_6$$ and excess $$O_2$$ according to $$2\ C_6H_6 + 15\ O_2$ \rightarrow 12\ CO_2$ + 6\ H_2O. $$What is the percent yield of water?

Accepted Answer

28.8%

Question 11

If 115.0 g $$NH_3$$ reacts with $$OCl^- to $$produce $$N_2H_4$$ with an 81.5% yield, how many grams of $$N_2H_4$$ are produced? (Molar masses: $$NH_3 = 17.03$ g/mol, N_2H_4 = 32.05$ g/mol)

Accepted Answer

88.0 g

Question 12

Which of the following statements about the actual yield is correct?

Accepted Answer

It is always less than the theoretical yield due to inefficiencies in real reactions.

Question 13

In the reaction $$Fe_2O_3 (s) + 3 H_2$ (g) \rightarrow 2 Fe (s) + 3 H_2O (g)$$, how many moles of $$Fe_2O_3$$ are required to produce 0.850 moles of Fe if the reaction is only 75% complete?

Accepted Answer

0.567 mol

Question 14

Which of the following is a correct step when determining the limiting reagent in a reaction?

Accepted Answer

Convert the given quantities of each reactant into moles

Question 15

A reaction between solid aluminum and iron (III) oxide is used in welding. If 150 g of Al are reacted with 432 g of $$Fe_2O_3$$, what is the mass of the excess reactant remaining? (Molar masses: Al = 26.98 g/mol, $$Fe_2O_3 = 159.7 g/$$mol)

Accepted Answer

16.2 g

Question 16

Which of the following is a real-world application of stoichiometry?

Accepted Answer

Calculating the amount of fertilizer needed for a specific crop yield

Chemical Reactions and Chemical Quantities: Balancing, Stoichiometry, Limiting Reagents, and Percent Yield

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