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

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

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 number of atoms of each element must be the same on both sides of a balanced chemical equation.

Question 2

Given the unbalanced equation for the combustion of propane: $$\mathrm{C_3H_8} + \mathrm{O_2$} \rightarrow \mathrm{CO_2$} + \mathrm{H_2O}$$, what are the correct stoichiometric coefficients (in order: $$\mathrm{C_3H_8}$$, $$\mathrm{O_2$}$$, $$\mathrm{CO_2$}$$, $$\mathrm{H_2O}) $$when the equation is balanced?

Accepted Answer

$$1, 5, 3, 4$$

Question 3

A plant carries out photosynthesis according to the equation: $$6\mathrm{CO_2$} + 6\mathrm{H_2O} \rightarrow \mathrm{C_6H_{12}O_6$} + 6\mathrm{O_2$}. If a $$plant consumes $$7.5\ \mathrm{g} of$$ $$\mathrm{CO_2$} in $$one week, what is the maximum mass of glucose ($$\mathrm{C_6H_{12}O_6$}$$, molar mass $$=180\ \mathrm{g/mol}) $$that can be synthesized? (Molar mass of $$\mathrm{CO_2$} is$$ $$44.01\ \mathrm{g/mol})$$

Accepted Answer

$$5.1\ \mathrm{g}$$

Question 4

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

Accepted Answer

It is the reactant that is completely consumed first, thus limiting the amount of product formed.

Question 5

Consider the reaction: $$2\mathrm{NO}(g) + 5\mathrm{H_2$}(g) \rightarrow 2\mathrm{NH_3$}(g) + 2\mathrm{H_2O}(g). If$$ $$86.3\ \mathrm{g} of$$ $$\mathrm{NO} ($$molar mass $$=30.01\ \mathrm{g/mol}) $$and $$25.6\ \mathrm{g} of$$ $$\mathrm{H_2$} ($$molar mass $$=2.02\ \mathrm{g/mol}) $$are reacted, what is the theoretical yield of ammonia ($$\mathrm{NH_3$}$$, molar mass $$=17.03\ \mathrm{g/mol}) in $$grams?

Accepted Answer

$$49.0\ \mathrm{g}$$

Question 6

A reaction has a theoretical yield of $$45.8\ \mathrm{g}$$, but only $$37.2\ \mathrm{g} of $$product is actually obtained. What is the percent yield?

Accepted Answer

$$81.2\%$$

Question 7

Which of the following is the correct balanced equation for the reaction between solid cobalt(III) oxide and solid carbon to produce solid cobalt and carbon dioxide gas?

Accepted Answer

$$2\mathrm{Co_2O_3}(s) + 3\mathrm{C}(s) \rightarrow 4\mathrm{Co}(s) + 3\mathrm{CO_2$}(g)$$

Question 8

In a reaction vessel, $$2.8$$ mol of $$\mathrm{H_2$} is $$mixed with $$3.2$$ mol of $$\mathrm{F_2$}$$ according to the reaction $$\mathrm{H_2$} + \mathrm{F_2$} \rightarrow 2\mathrm{HF}. $$What is the limiting reagent and what is the theoretical yield of $$\mathrm{HF} in $$moles?

Accepted Answer

$$\mathrm{H_2$} is $$the limiting reagent; theoretical yield is $$5.6$$ mol

Question 9

Which of the following is the correct formula to calculate the number of moles $$n$$ from mass $$m$$ and molar mass $$MM$$?

Accepted Answer

$$n = \frac{m}{MM}$$

Question 10

A mixture of propane ($$\mathrm{C_3H_8}) $$and acetylene ($$\mathrm{C_2H_2}) $$has a total mass of $$2.0\ \mathrm{g}. $$When burned in excess oxygen, the mixture produces $$1.5$$ times as many molecules of $$\mathrm{CO_2$} as$$ $$\mathrm{H_2O}. $$Which statement best describes the approach to determine the mass of acetylene in the mixture?

Accepted Answer

Set up and solve a system of equations using the combustion reactions for both hydrocarbons and the given ratio of $$\mathrm{CO_2$} to$$ $$\mathrm{H_2O}.$$

Question 11

Which of the following is the correct balanced equation for the combustion of butane ($$\mathrm{C_4H_{10}}$$)?

Accepted Answer

$$2\mathrm{C_4H_{10}}(g) + 13\mathrm{O_2$}(g) \rightarrow 8\mathrm{CO_2$}(g) + 10\mathrm{H_2O}(g)$$

Question 12

If $$55.0\ \mathrm{g} of $$sodium reacts with $$67.2\ \mathrm{g} of $$chlorine gas according to $$2\mathrm{Na} + \mathrm{Cl_2$} \rightarrow 2\mathrm{NaCl}$$, what is the theoretical yield of sodium chloride? (Molar masses: $$\mathrm{Na} = 23.00\ \mathrm{g/mol}$$, $$\mathrm{Cl_2$} = 70.91\ \mathrm{g/mol}$$, $$\mathrm{NaCl} = 58.44\ \mathrm{g/mol})$$

Accepted Answer

$$111\ \mathrm{g}$$

Question 13

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

Accepted Answer

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

Question 14

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

Accepted Answer

Balance hydrogen and oxygen atoms first before all other elements.

Question 15

A sample of $$25.0\ \mathrm{g} of$$ $$\mathrm{$$MnO_2$$} ($$molar mass $$=86.94\ \mathrm{g/mol}) $$reacts with excess aluminum according to $$3\mathrm{$$MnO_2$$} + 4\mathrm{Al} \rightarrow 3\mathrm{Mn} + 2\mathrm{Al_2O_3}. $$What mass of aluminum (molar mass $$=26.98\ \mathrm{g/mol}) is $$required to completely react with the $$\mathrm{$$MnO_2$$}$$?

Accepted Answer

$$7.76\ \mathrm{g}$$

Question 16

Which of the following best explains why the mass of glucose produced in photosynthesis is less than the total mass of carbon dioxide consumed?

Accepted Answer

Each carbon atom in $$\mathrm{CO_2$} is $$associated with two oxygen atoms, while in glucose each carbon is associated with only one oxygen atom and two hydrogen atoms, which are lighter.

Question 17

Which of the following is the correct balanced equation for the reaction between aqueous strontium chloride and lithium phosphate to form solid strontium phosphate and aqueous lithium chloride?

Accepted Answer

$$3\mathrm{$$SrCl_2$$}(aq) + 2\mathrm{Li_3PO_4}(aq) \rightarrow \mathrm{Sr_3$(PO_4$)_2}(s) + 6\mathrm{LiCl}(aq)$$

Chapter 4: Chemical Reactions and Chemical Quantities – General Chemistry 1

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