Q: Which of the following equations correctly expresses percent yield?

$$\displaystyle \frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$$

Question 1

Which of the following best describes the greenhouse effect as it relates to Earth's atmosphere?

Accepted Answer

Greenhouse gases allow sunlight to enter, warm Earth's surface, and trap some heat radiated from the surface.

Question 2

Which of the following is a balanced chemical equation for the combustion of methane?

Accepted Answer

$$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(g)}$$

Question 3

In the reaction $$2\mathrm{C_8H_{18}(l) + 25O_2(g) \rightarrow 16CO_2(g) + 18H_2O(g)}$$, how many moles of $$\mathrm{CO_2$}$$ are produced from burning 22.0 moles of $$\mathrm{C_8H_{18}}$$?

Accepted Answer

176 moles

Question 4

Which quantity must always be the same on both sides of a balanced chemical equation?

Accepted Answer

The number of atoms of each kind

Question 5

A car engine burns octane ($$\mathrm{C_8H_{18}}) $$according to the equation $$2\mathrm{C_8H_{18}(l) + 25O_2(g) ightarrow 16CO_2(g) + 18H_2O(g)}. $$What mass of $$\mathrm{CO_2$} (in g) is $$produced from burning $$4.0 	imes 10$$^{15}$$ g of $$\mathrm{C_8H_{18}}$$? (Molar masses: $$\mathrm{C_8H_{18}} = 114.22$$ g/mol, $$\mathrm{$$CO_2$$} = 44.01$$ g/mol)

Accepted Answer

$$1.2 	imes 10$$^{16}$$ g

Question 6

Which of the following best defines the limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed and limits the amount of product formed

Question 7

If 3.26 g of $$\mathrm{Mg(OH)_2} is $$used to neutralize stomach acid, what mass of $$\mathrm{HCl} (in g) is $$neutralized? (Molar masses: $$\mathrm{Mg(OH)_2} = 58.32 g/$$mol, $$\mathrm{HCl} = 36.46 g/$$mol, reaction: $$\mathrm{Mg(OH)_2 + 2HCl \rightarrow $$MgCl_2$$ + 2H_2O})$$

Accepted Answer

4.08 g

Question 8

A reaction mixture contains 42.5 g Mg and 33.8 g $$\mathrm{O_2$}. $$According to the reaction $$2\mathrm{Mg(s) + O_2$(g) \rightarrow 2MgO(s)}$$, what is the limiting reactant?

Accepted Answer

$$\mathrm{Mg}$$

Question 9

Which of the following equations correctly expresses percent yield?

Accepted Answer

$$\displaystyle \frac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100\%$$

Question 10

Which of the following reactions is an example of a combustion reaction?

Accepted Answer

$$\mathrm{CH_4$(g) + 2O_2(g) \rightarrow CO_2$(g) + 2H_2O(g)}$$

Question 11

Upon combustion of 0.8009 g of a compound containing only C, H, and O, 1.6004 g of $$\mathrm{CO_2$}$$ and 0.6551 g of $$\mathrm{H_2O}$$ are produced. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{C_2H_4O}$$

Question 12

Which of the following best describes the reaction of alkali metals with water?

Accepted Answer

They form dissolved alkali metal ions, hydroxide ions, and hydrogen gas.

Question 13

Which of the following statements about the reaction $$2\mathrm{NO_2$(g) + H_2O(l) \rightarrow 2HNO_3(l) + NO(g)} is $$correct if 5 mol $$\mathrm{NO_2$}$$ and 1 mol $$\mathrm{H_2O}$$ are combined?

Accepted Answer

2 mol $$\mathrm{NO_2$}$$ remain in excess after the reaction.

Question 14

Which of the following is a correct statement about the Law of Conservation of Mass as it applies to chemical reactions?

Accepted Answer

The total number of atoms of each element is conserved during a chemical reaction.

Question 15

Which of the following best describes a combustion reaction?

Accepted Answer

A reaction in which a substance combines with oxygen to form one or more oxygen-containing compounds and emits heat.

Question 16

A sample of $$\mathrm{Fe_2O_3} (167 g) $$reacts with 85.0 g CO and produces 72.3 g Fe. What is the percent yield of Fe? (Theoretical yield = 113 g)

Accepted Answer

64%

Question 17

Which of the following is a correct balanced equation for the reaction of sodium with chlorine gas?

Accepted Answer

$$\mathrm{2Na(s) + Cl_2$(g) \rightarrow 2NaCl(s)}$$

Question 18

Which of the following is a correct description of an excess reactant?

Accepted Answer

A reactant that remains after the limiting reactant is used up.

Chapter 4: Chemical Reactions and Chemical Quantities – Study Guide

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