Q: Which of the following is the correct formula for calculating percent yield in a chemical reaction?

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

Question 1

Which of the following best describes 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.

Question 2

A student burns 22.0 moles of octane ($$\mathrm{C_8H_{18}}) in $$excess oxygen. According to the balanced equation $$2\ \mathrm{C_8H_{18}} + 25\ \mathrm{O_2$} \rightarrow 16\ \mathrm{CO_2$} + 18\ \mathrm{H_2O}$$, how many moles of $$\mathrm{CO_2$}$$ are produced?

Accepted Answer

$$176$$ moles

Question 3

Which of the following is the correct formula for calculating percent yield in a chemical reaction?

Accepted Answer

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

Question 4

Which reactant limits the amount of product formed in a chemical reaction?

Accepted Answer

The limiting reactant.

Question 5

Combustion reactions are characterized by which of the following?

Accepted Answer

A substance reacts with oxygen to form one or more oxygen-containing compounds and emits heat.

Question 6

Which of the following best explains the greenhouse effect as shown in the provided diagram?

Accepted Answer

Greenhouse gases trap some of the heat radiated from Earth's surface, warming the planet.

Question 7

Given the reaction $$2\ \mathrm{Na} + 2\ \mathrm{H_2O} \rightarrow 2\ \mathrm{NaOH} + \mathrm{H_2$}$$, what is the theoretical yield of $$\mathrm{H_2$} (in $$moles) if 4.6 g of Na (molar mass = 23.0 g/mol) reacts with excess water?

Accepted Answer

$$0.10$$ mol

Question 8

Which of the following statements about balancing chemical equations is correct?

Accepted Answer

You must balance the equation by changing the coefficients, not the subscripts.

Question 9

A reaction mixture contains 42.5 g of magnesium (Mg, molar mass = 24.3 g/mol) and 33.8 g of oxygen gas ($$\mathrm{O_2$}$$, molar mass = 32.0 g/mol). The reaction is $$2\ \mathrm{Mg} + \mathrm{O_2$} \rightarrow 2\ \mathrm{MgO}. $$What is the limiting reactant?

Accepted Answer

Oxygen gas

Question 10

Which of the following is a correct example of a halogen reaction?

Accepted Answer

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

Question 11

If the actual yield of a reaction is 5.0 g and the theoretical yield is 8.0 g, what is the percent yield?

Accepted Answer

$$62.5\%$$

Question 12

Which of the following best describes the trend in atmospheric carbon dioxide concentration from 1880 to 2020, as shown in the graph?

Accepted Answer

It increased significantly.

Question 13

Which of the following is NOT a characteristic of combustion reactions?

Accepted Answer

They always produce carbon dioxide and water.

Question 14

A car burns octane ($$\mathrm{C_8H_{18}}) as $$fuel. If 1.00 kg of octane is completely combusted, how many grams of $$\mathrm{CO_2$}$$ are produced? (Molar mass: $$\mathrm{C_8H_{18}} = 114 g/$$mol, $$\mathrm{CO_2$} = 44 g/$$mol; $$2\ \mathrm{C_8H_{18}} + 25\ \mathrm{O_2$} \rightarrow 16\ \mathrm{CO_2$} + 18\ \mathrm{H_2O})$$

Accepted Answer

$$6.16 kg$$

Question 15

Which of the following best explains why the reaction of alkali metals with water becomes more vigorous as you move down the group?

Accepted Answer

The ionization energy decreases, making it easier to lose an electron.

Question 16

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

Accepted Answer

2 moles of $$\mathrm{C_8H_{18}}$$ produce 16 moles of $$\mathrm{CO_2$}$$

Question 17

Which of the following is a correct statement about the actual yield in a chemical reaction?

Accepted Answer

It is the amount of product actually produced in the reaction.

Question 18

Which of the following best describes the trend in global temperature from 1880 to 2020, as shown in the graph?

Accepted Answer

It increased overall, with some fluctuations.

Question 19

Which of the following is a correct example of a reaction between halogens and hydrogen?

Accepted Answer

$$\mathrm{H_2$} + \mathrm{Cl_2$} \rightarrow 2\ \mathrm{HCl}$$

Chemical Reactions and Chemical Quantities: Core Concepts and Applications

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