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: Which of the following is a correct sequence for a mass-to-mass stoichiometric calculation?

$$\text{Mass A} \rightarrow \text{Moles A} \rightarrow \text{Moles B} \rightarrow \text{Mass B}$$

Question 1

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, often releasing heat.

Question 2

Given the unbalanced equation: $$\mathrm{C_2H_6} + \mathrm{O_2$} \rightarrow \mathrm{CO_2$} + \mathrm{H_2O}$$, what is the correct set of coefficients to balance the equation?

Accepted Answer

$$2, 7, 4, 6$$

Question 3

In the reaction $$\mathrm{CH_4$(g) + 2 O_2$(g) \rightarrow CO_2$(g) + 2 H_2O(g)}$$, how many moles of $$\mathrm{O_2$}$$ are required to completely react with 5 moles of $$\mathrm{CH_4$}$$?

Accepted Answer

$$10$$ moles

Question 4

Which statement about balancing chemical equations is correct?

Accepted Answer

Coefficients are changed to balance the equation, but subscripts must never be changed.

Question 5

A reaction mixture contains 42.5 g Mg and 33.8 g O$$_2. $$The balanced equation is $$2\mathrm{Mg} + \mathrm{O_2$} \rightarrow 2\mathrm{MgO}. $$What is the limiting reactant?

Accepted Answer

Mg

Question 6

If the theoretical yield of MgO in the reaction above is 70.5 g and the actual yield is 66.3 g, what is the percent yield?

Accepted Answer

$$94.0\%$$

Question 7

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 8

In a combustion analysis, a 1.00 g sample of a hydrocarbon produces 3.14 g CO$$_2$$ and 1.29 g H$$_2O. $$What is the empirical formula of the hydrocarbon?

Accepted Answer

$$\mathrm{C_3H_8}$$

Question 9

Which of the following is a correct mole-to-mole conversion factor for the reaction $$2\mathrm{C_8H_{18}} + 25\mathrm{O_2$} \rightarrow 16\mathrm{CO_2$} + 18\mathrm{H_2O}$$?

Accepted Answer

$$\frac{16\ \mathrm{mol\ CO_2$}}{2\ \mathrm{mol\ C_8H_{18}}}$$

Question 10

A student mixes 4 crusts, 10 cups of cheese, and 15 ounces of tomato sauce to make pizzas. If each pizza requires 1 crust, 2 cups of cheese, and 5 ounces of tomato sauce, what is the limiting reactant?

Accepted Answer

Tomato sauce

Question 11

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 12

Which of the following statements about stoichiometry is correct?

Accepted Answer

Stoichiometry is the numerical relationship between chemical amounts in a balanced chemical equation.

Question 13

Which of the following is a correct sequence for a mass-to-mass stoichiometric calculation?

Accepted Answer

$$	ext{Mass A} ightarrow 	ext{Moles A} ightarrow 	ext{Moles B} ightarrow 	ext{Mass B}$$

Question 14

Which of the following reactions is an example of a halogen reacting with a metal?

Accepted Answer

$$2\mathrm{Na} + \mathrm{Cl_2$} \rightarrow 2\mathrm{NaCl}$$

Question 15

A sample of propane ($$\mathrm{C_3H_8}) is $$combusted in excess oxygen. If 44.0 g of $$\mathrm{CO_2$} is $$produced, how many grams of $$\mathrm{C_3H_8}$$ were combusted? (Molar masses: $$\mathrm{C_3H_8} = 44.1 g/$$mol, $$\mathrm{CO_2$} = 44.0 g/$$mol)$$

\mathrm{C_3H_8} + 5\mathrm{O_2$} \rightarrow 3\mathrm{CO_2$} + 4\mathrm{H_2O}$$

Accepted Answer

$$14.7 g$$

Question 16

Which of the following best explains why the actual yield of a reaction is usually less than the theoretical yield?

Accepted Answer

Some product is lost during recovery or side reactions may occur.

Question 17

Which of the following is true about alkali metal reactions with water?

Accepted Answer

Heavier alkali metals react more vigorously with water than lighter ones.

Question 18

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 mass of reactants equals the total mass of products in a chemical reaction.

Chapter 4: Chemical Reactions and Chemical Quantities – Study Notes

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