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

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

Question 1

Which of the following statements best describes the Law of Conservation of Mass as it applies to chemical reactions?

Accepted Answer

The total mass of each element on the reactant side must equal the total mass of each element on the product side.

Question 2

What is the correct balanced chemical equation for the combustion of methane ($$CH_4) in $$oxygen?

Accepted Answer

$$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$

Question 3

In the reaction $$2H_2 + O_2$ \rightarrow 2H_2O$$, how many grams of water are produced from 4.04 g of $$H_2$$ and excess $$O_2$$? (Molar mass $$H_2 = 2.02$ g/mol, H_2O = 18.0$ g/mol)

Accepted Answer

$$36.0 g$$

Question 4

Which of the following is NOT a correct rule for balancing chemical equations?

Accepted Answer

Change the subscripts in chemical formulas to balance the equation.

Question 5

A student burns 10.0 g of methane ($$CH_4) in 30.0 g of $$oxygen ($$O_2) to $$produce carbon dioxide and water. Which reactant is limiting? (Molar mass $$CH_4 = 16.0$ g/mol, O_2$ = 32.0 g/$$mol)

Accepted Answer

$$O_2$$

Question 6

What is the percent yield if 6.0 g of aluminum reacts with excess bromine to produce 50.3 g of aluminum bromide ($$AlBr_3$$)? (Molar mass $$Al = 27.0 g/$$mol, $$AlBr_3 = 266.7$ g/mol)

Accepted Answer

$$64.6\%$$

Question 7

Which of the following best describes a combustion reaction?

Accepted Answer

A reaction between oxygen and another substance, typically producing $$CO_2$$ and $$H_2O.$$

Question 8

In the reaction $$2Na(s) + 2H_2O(l) \rightarrow 2Na^+(aq) + 2OH^-(aq) + H_2$(g)$$, what is the state of $$Na^+ in $$the products?

Accepted Answer

Aqueous (aq)

Question 9

A reaction produces 10.0 g of $$CO_2$$ from sodium carbonate and hydrochloric acid. How many grams of $$HCl$$ are required? ($$Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2$, Molar mass CO_2$ = 44.0 g/$$mol, $$HCl = 36.5 g/$$mol)

Accepted Answer

$$16.6 g$$

Question 10

Which of the following is a correct mole-to-mole ratio for the reaction $$2H_2 + O_2$ \rightarrow 2H_2O$$?

Accepted Answer

$$2$$ mol $$H_2$$ : $$1$$ mol $$O_2$$ : $$2$$ mol $$H_2O$$

Question 11

Which of the following is a possible reason for a percent yield less than 100%?

Accepted Answer

Impure product or incomplete reaction.

Question 12

In the reaction $$P_4 + 6Cl_2$$ \rightarrow 4PCl_3$$, what mass of $$PCl_3$$ is formed from 125 g P_4$ and 323 g Cl_2$? (Molar mass P_4$ = 124 g/$$mol, $$Cl_2 = 71$ g/mol, $$PCl_3$$ = 137.5 g/$$mol)

Accepted Answer

$$412 g$$

Question 13

Which of the following is the correct interpretation of the symbol $$(aq) in a $$chemical equation?

Accepted Answer

Dissolved in water

Question 14

Which of the following is the correct formula for a generic hydrocarbon?

Accepted Answer

$$C_xH_y$$

Question 15

Which of the following is a correct statement about limiting reactants?

Accepted Answer

The limiting reactant determines the maximum amount of product formed.

Question 16

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

Accepted Answer

$$2Fe(s) + 3Cl_2(g) \rightarrow 2FeCl_3(s)$$

Question 17

If a chemical equation is not balanced, which law is violated?

Accepted Answer

Law of Conservation of Mass

Question 18

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

Accepted Answer

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

Question 19

Which of the following is a correct step in solving a stoichiometry problem involving mass-to-mass conversion?

Accepted Answer

Convert mass of reactant to moles using molar mass.

Chapter 4: Chemical Reactions and Chemical Quantities – Study Notes

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