Q: For the reaction $$2\mathrm{Co}_2\mathrm{O}_3(s) + 3\mathrm{C}(s) \rightarrow 4\mathrm{Co}(s) + 3\mathrm{CO}_2(g)$$, how many moles of carbon are required to react completely with $$10$$ moles of $$\mathrm{Co}_2\mathrm{O}_3$$?

$$10 \text{ mol} \times \frac{3 \text{ mol C}}{2 \text{ mol } \mathrm{Co}_2\mathrm{O}_3}} = 15 \text{ mol C}$$

Q: A student combusts $$5.0 \times 10^2$ g of octane ($$\mathrm{C}_8\mathrm{H}_{18}$$). Using the balanced equation 2$$\mathrm{C}_8\mathrm{H}_{18}(l) + 25\mathrm{O}_2(g) \rightarrow 16\mathrm{CO}_2(g) + 18\mathrm{H}_2\mathrm{O}(g)$$, what mass of $$\mathrm{CO}_2$$ is produced? (Molar masses: $$\mathrm{C}_8\mathrm{H}_{18} = 114.3$$ g/mol, $$\mathrm{CO}_2 = 44.01$$ g/mol)

$$5.0 \times 10^2$ \text{ g} \times \frac{1 \text{ mol}}{114.3 \text{ g}} \times \frac{16 \text{ mol } \mathrm{CO}_2}{2 \text{ mol } \mathrm{C}_8\mathrm{H}_{18}} \times \frac{44.01 \text{ g}}{1 \text{ mol } \mathrm{CO}_2} = 1.5 \times 10^3$ \text{ g}$$

Q: In the reaction $$\mathrm{Mg(OH)}_2(aq) + 2\mathrm{HCl}(aq) \rightarrow 2\mathrm{H}_2\mathrm{O}(l) + \mathrm{MgCl}_2(aq)$$, how many grams of $$\mathrm{HCl}$$ can be neutralized by $$5.50 g of$$ $$\mathrm{Mg(OH)}_2$$? (Molar masses: $$\mathrm{Mg(OH)}_2 = 58.32 g/$$mol, $$\mathrm{HCl} = 36.46 g/$$mol)

$$5.50 \text{ g} \times \frac{1 \text{ mol}}{58.32 \text{ g}} \times \frac{2 \text{ mol HCl}}{1 \text{ mol Mg(OH)}_2} \times \frac{36.46 \text{ g}}{1 \text{ mol HCl}} = 6.88 \text{ g}$$

Q: A reaction has a theoretical yield of $$108 g of$$ $$\mathrm{NaCl}$$, but only $$86.4 g is $$actually produced. What is the percent yield?

$$\frac{86.4 \text{ g}}{108 \text{ g}} \times 100\% = 80.0\%$$

Q: If $$25.0 g of$$ $$\mathrm{CH}_4 is $$combusted according to $$\mathrm{CH}_4(g) + 2\mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + 2\mathrm{H}_2\mathrm{O}(g)$$ with $$\Delta H_{rxn} = -802 kJ$$, how much heat is released? (Molar mass $$\mathrm{CH}_4 = 16.05 g/$$mol)

$$25.0 \text{ g} \times \frac{1 \text{ mol}}{16.05 \text{ g}} \times \frac{-802 \text{ kJ}}{1 \text{ mol}} = -1.25 \times 10^3$ \text{ kJ}$$

Q: In the photosynthesis reaction $$6\mathrm{CO}_2(g) + 6\mathrm{H}_2\mathrm{O}(l) \rightarrow 6\mathrm{O}_2(g) + \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6(aq)$$, how many grams of glucose ($$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6) $$are produced from $$58.5 g of$$ $$\mathrm{CO}_2$$? (Molar masses: $$\mathrm{CO}_2 = 44.01 g/$$mol, $$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 = 180.2 g/$$mol)

$$58.5 \text{ g} \times \frac{1 \text{ mol}}{44.01 \text{ g}} \times \frac{1 \text{ mol } \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6}{6 \text{ mol } \mathrm{CO}_2} \times \frac{180.2 \text{ g}}{1 \text{ mol } \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6} = 39.9 \text{ g}$$

Question 1

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

Accepted Answer

The reactant that is completely consumed first, thus limiting the amount of product that can be formed.

Question 2

For the reaction $$2\mathrm{Co}_2\mathrm{O}_3(s) + 3\mathrm{C}(s) \rightarrow 4\mathrm{Co}(s) + 3\mathrm{CO}_2(g)$$, how many moles of carbon are required to react completely with $$10$$ moles of $$\mathrm{Co}_2\mathrm{O}_3$$?

Accepted Answer

$$10 	ext{ mol} 	imes \frac{3 	ext{ mol C}}{2 	ext{ mol } \mathrm{Co}_2\mathrm{O}_3}} = 15 	ext{ mol C}$$

Question 3

A student combusts $$5.0 	imes 10^2$ g of octane ($$\mathrm{C}_8\mathrm{H}_{18}$$). Using the balanced equation 2$$\mathrm{C}_8\mathrm{H}_{18}(l) + 25\mathrm{O}_2(g) ightarrow 16\mathrm{CO}_2(g) + 18\mathrm{H}_2\mathrm{O}(g)$$, what mass of $$\mathrm{CO}_2$$ is produced? (Molar masses: $$\mathrm{C}_8\mathrm{H}_{18} = 114.3$$ g/mol, $$\mathrm{CO}_2 = 44.01$$ g/mol)

Accepted Answer

$$5.0 	imes 10^2$ 	ext{ g} 	imes \frac{1 	ext{ mol}}{114.3 	ext{ g}} 	imes \frac{16 	ext{ mol } \mathrm{CO}_2}{2 	ext{ mol } \mathrm{C}_8\mathrm{H}_{18}} 	imes \frac{44.01 	ext{ g}}{1 	ext{ mol } \mathrm{CO}_2} = 1.5 	imes 10^3$ 	ext{ g}$$

Question 4

In the reaction $$\mathrm{Mg(OH)}_2(aq) + 2\mathrm{HCl}(aq) \rightarrow 2\mathrm{H}_2\mathrm{O}(l) + \mathrm{MgCl}_2(aq)$$, how many grams of $$\mathrm{HCl}$$ can be neutralized by $$5.50 g of$$ $$\mathrm{Mg(OH)}_2$$? (Molar masses: $$\mathrm{Mg(OH)}_2 = 58.32 g/$$mol, $$\mathrm{HCl} = 36.46 g/$$mol)

Accepted Answer

$$5.50 	ext{ g} 	imes \frac{1 	ext{ mol}}{58.32 	ext{ g}} 	imes \frac{2 	ext{ mol HCl}}{1 	ext{ mol Mg(OH)}_2} 	imes \frac{36.46 	ext{ g}}{1 	ext{ mol HCl}} = 6.88 	ext{ g}$$

Question 5

A reaction has a theoretical yield of $$108 g of$$ $$\mathrm{NaCl}$$, but only $$86.4 g is $$actually produced. What is the percent yield?

Accepted Answer

$$\frac{86.4 	ext{ g}}{108 	ext{ g}} 	imes 100\% = 80.0\%$$

Question 6

For the reaction $$2\mathrm{NO}(g) + 5\mathrm{H}_2(g) \rightarrow 2\mathrm{NH}_3(g) + 2\mathrm{H}_2\mathrm{O}(g)$$, if you start with $$4.0$$ mol of $$\mathrm{NO}$$ and $$15.0$$ mol of $$\mathrm{H}_2$$, what is the limiting reactant and how many moles of $$\mathrm{NH}_3$$ are formed?

Accepted Answer

$$\mathrm{NO} is $$the limiting reactant; $$4.0$$ mol $$\mathrm{NH}_3$$ are formed.

Question 7

The combustion of methane is represented by $$\mathrm{CH}_4(g) + 2\mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + 2\mathrm{H}_2\mathrm{O}(g)$$ with $$\Delta H_{rxn} = -802.3 kJ. $$What does the negative sign of $$\Delta H_{rxn}$$ indicate?

Accepted Answer

The reaction is exothermic and releases $$802.3 kJ of $$heat per mole of $$\mathrm{CH}_4$$ combusted.

Question 8

A chemical reaction has $$\Delta H_{rxn} = +182.6 kJ. $$Which of the following statements is true?

Accepted Answer

The reaction is endothermic and absorbs $$182.6 kJ of $$heat from the surroundings.

Question 9

If $$25.0 g of$$ $$\mathrm{CH}_4 is $$combusted according to $$\mathrm{CH}_4(g) + 2\mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + 2\mathrm{H}_2\mathrm{O}(g)$$ with $$\Delta H_{rxn} = -802 kJ$$, how much heat is released? (Molar mass $$\mathrm{CH}_4 = 16.05 g/$$mol)

Accepted Answer

$$25.0 	ext{ g} 	imes \frac{1 	ext{ mol}}{16.05 	ext{ g}} 	imes \frac{-802 	ext{ kJ}}{1 	ext{ mol}} = -1.25 	imes 10^3$ 	ext{ kJ}$$

Question 10

In the photosynthesis reaction $$6\mathrm{CO}_2(g) + 6\mathrm{H}_2\mathrm{O}(l) \rightarrow 6\mathrm{O}_2(g) + \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6(aq)$$, how many grams of glucose ($$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6) $$are produced from $$58.5 g of$$ $$\mathrm{CO}_2$$? (Molar masses: $$\mathrm{CO}_2 = 44.01 g/$$mol, $$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 = 180.2 g/$$mol)

Accepted Answer

$$58.5 	ext{ g} 	imes \frac{1 	ext{ mol}}{44.01 	ext{ g}} 	imes \frac{1 	ext{ mol } \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6}{6 	ext{ mol } \mathrm{CO}_2} 	imes \frac{180.2 	ext{ g}}{1 	ext{ mol } \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6} = 39.9 	ext{ g}$$

Question 11

A reaction $$2\mathrm{A} + 3\mathrm{B} \rightarrow 2\mathrm{C}$$ has $$\Delta H_{rxn} = -100 kJ. If $$you start with $$5$$ mol of $$\mathrm{A}$$ and $$6$$ mol of $$\mathrm{B}$$, how much heat is evolved?

Accepted Answer

$$3 	ext{ mol B} ightarrow 100 	ext{ kJ}$$, so $$6 	ext{ mol B} ightarrow 200 	ext{ kJ}$$; $$200 kJ of $$heat is evolved.

Question 12

Which of the following best explains why burning fossil fuels contributes to climate change?

Accepted Answer

Combustion of fossil fuels increases atmospheric $$\mathrm{CO}_2$$, a greenhouse gas that traps heat and raises Earth's temperature.

Question 13

In the reaction $$4\mathrm{NO}_2(g) + \mathrm{O}_2(g) + 2\mathrm{H}_2\mathrm{O}(l) ightarrow 4\mathrm{HNO}_3(aq)$$, how many kilograms of $$\mathrm{HNO}_3$$ are produced from $$1.5 	imes 10^3$ kg of $$\mathrm{NO}_2$$? (Molar masses: $$\mathrm{NO}_2 = 46.01$$ g/mol, $$\mathrm{HNO}_3 = 63.02$$ g/mol)

Accepted Answer

$$1.5 	imes 10^3$ 	ext{ kg} 	imes \frac{1000 	ext{ g}}{1 	ext{ kg}} 	imes \frac{1 	ext{ mol}}{46.01 	ext{ g}} 	imes \frac{4 	ext{ mol HNO}_3}{4 	ext{ mol NO}_2} 	imes \frac{63.02 	ext{ g}}{1 	ext{ mol HNO}_3} 	imes \frac{1 	ext{ kg}}{1000 	ext{ g}} = 2.05 	imes 10^3$ 	ext{ kg}$$

Question 14

A Bunsen burner is fueled by methane. Which adjustment will result in the hottest, cleanest flame?

Accepted Answer

Adjusting the air intake to produce a sharp, inner blue triangle with no smoke.

Question 15

For the reaction $$3\mathrm{H}_2(g) + \mathrm{N}_2(g) \rightarrow 2\mathrm{NH}_3(g)$$, how many moles of $$\mathrm{NH}_3$$ can be produced from $$3$$ moles of $$\mathrm{N}_2$$ with excess $$\mathrm{H}_2$$?

Accepted Answer

$$3 	ext{ mol } \mathrm{N}_2 	imes \frac{2 	ext{ mol } \mathrm{NH}_3}{1 	ext{ mol } \mathrm{N}_2} = 6 	ext{ mol } \mathrm{NH}_3$$

Question 16

A reaction $$A + 2B \rightarrow 3C is $$carried out with equal masses of $$A$$ and $$B. If $$the molar mass of $$B is $$greater than that of $$A$$, which is the limiting reactant?

Accepted Answer

$$B is $$the limiting reactant because it has fewer moles for the same mass.

Question 17

For the reaction $$4\mathrm{Na} + \mathrm{O}_2 \rightarrow 2\mathrm{Na}_2\mathrm{O}$$, how many moles of $$\mathrm{Na}_2\mathrm{O}$$ are produced from $$4.8$$ mol of $$\mathrm{Na}$$?

Accepted Answer

$$4.8 	ext{ mol Na} 	imes \frac{2 	ext{ mol Na}_2\mathrm{O}}{4 	ext{ mol Na}} = 2.4 	ext{ mol Na}_2\mathrm{O}$$

Question 18

A student reacts $$25.3 g of$$ $$\mathrm{N}_2$$ with $$8.42 g of$$ $$\mathrm{H}_2 to $$produce ammonia according to $$3\mathrm{H}_2(g) + \mathrm{N}_2(g) \rightarrow 2\mathrm{NH}_3(g). $$What is the theoretical yield of $$\mathrm{NH}_3 in $$grams? (Molar masses: $$\mathrm{N}_2 = 28.01 g/$$mol, $$\mathrm{H}_2 = 2.02 g/$$mol, $$\mathrm{NH}_3 = 17.0 g/$$mol)

Accepted Answer

$$25.3 	ext{ g N}_2 	imes \frac{1 	ext{ mol}}{28.01 	ext{ g}} = 0.9032 	ext{ mol N}_2$$; $$0.9032 	ext{ mol N}_2 	imes \frac{2 	ext{ mol NH}_3}{1 	ext{ mol N}_2} = 1.8064 	ext{ mol NH}_3$$; $$1.8064 	ext{ mol NH}_3 	imes 17.0 	ext{ g/mol} = 30.7 	ext{ g NH}_3$$

Ch 8: Stoichiometry, Limiting Reactants, and Enthalpy in Chemical Reactions

Study Guide - Practice Questions

Study Guide - Flashcards