Q: If you have 5.0 $$\times$$ $$10^2 g of $$pure octane ($$\mathrm{C}_8\mathrm{H}_{18}$$), what mass of $$\mathrm{CO}_2 is $$emitted according to the equation $$2\ \mathrm{C}_8\mathrm{H}_{18}(l) + 25\ \mathrm{O}_2(g) \rightarrow 16\ \mathrm{CO}_2(g) + 18\ \mathrm{H}_2\mathrm{O}(g)$$? (Molar masses: $$\mathrm{C}_8\mathrm{H}_{18} = 114.3 g/$$mol, $$\mathrm{CO}_2 = 44.01 g/$$mol)

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

Q: A chemical reaction produced 87.4 g of copper, but the theoretical yield was 101.7 g. What is the percent yield?

$$\frac{87.4\ \mathrm{g}}{101.7\ \mathrm{g}} \times 100\% = 85.9\%$$

Q: Which equation correctly represents the calculation of percent yield?

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

Q: A propane tank contains $$1.18 \times 10^4$ g of $$\mathrm{C}_3\mathrm{H}_8$$. How much heat is released upon complete combustion? (Molar mass $$\mathrm{C}_3\mathrm{H}_8$$ = 44.11 g/mol, $$\Delta H_{rxn} = -2044$$ kJ/mol)

$$1.18 \times 10^4$\ \mathrm{g}\ \mathrm{C}_3\mathrm{H}_8 \times \frac{1\ \mathrm{mol}\ \mathrm{C}_3\mathrm{H}_8}{44.11\ \mathrm{g}\ \mathrm{C}_3\mathrm{H}_8} \times \frac{-2044\ \mathrm{kJ}}{1\ \mathrm{mol}\ \mathrm{C}_3\mathrm{H}_8} = -5.47 \times 10^5$\ \mathrm{kJ}$$

Q: If 155 g of $$\mathrm{NH}_3$$ reacts completely according to $$4\ \mathrm{NH}_3(g) + 5\ \mathrm{O}_2(g) \rightarrow 4\ \mathrm{NO}(g) + 6\ \mathrm{H}_2\mathrm{O}$$ ($$\Delta H_{rxn} = -906 kJ$$), what is the heat released? (Molar mass $$\mathrm{NH}_3 = 17.03 g/$$mol)

$$155\ \mathrm{g}\ \mathrm{NH}_3 \times \frac{1\ \mathrm{mol}\ \mathrm{NH}_3}{17.03\ \mathrm{g}\ \mathrm{NH}_3} \times \frac{-906\ \mathrm{kJ}}{4\ \mathrm{mol}\ \mathrm{NH}_3} = -2060\ \mathrm{kJ}$$

Question 1

Which of the following best describes the greenhouse effect as it relates to global warming?

Accepted Answer

Greenhouse gases allow visible-light energy to enter the atmosphere but prevent heat energy from escaping.

Question 2

Given the balanced equation for the combustion of octane: $$2\ \mathrm{C}_8\mathrm{H}_{18}(l) + 25\ \mathrm{O}_2(g) \rightarrow 16\ \mathrm{CO}_2(g) + 18\ \mathrm{H}_2\mathrm{O}(g)$$, how many moles of $$\mathrm{CO}_2$$ are produced from 4 moles of octane, assuming excess oxygen?

Accepted Answer

32 moles

Question 3

If you have 5.0 $$	imes$$ $$10^2 g of $$pure octane ($$\mathrm{C}_8\mathrm{H}_{18}$$), what mass of $$\mathrm{CO}_2 is $$emitted according to the equation $$2\ \mathrm{C}_8\mathrm{H}_{18}(l) + 25\ \mathrm{O}_2(g) ightarrow 16\ \mathrm{CO}_2(g) + 18\ \mathrm{H}_2\mathrm{O}(g)$$? (Molar masses: $$\mathrm{C}_8\mathrm{H}_{18} = 114.3 g/$$mol, $$\mathrm{CO}_2 = 44.01 g/$$mol)

Accepted Answer

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

Question 4

Which reactant is the limiting reactant when 53.2 g of Na and 65.8 g of $$\mathrm{Cl}_2$$ are reacted according to $$\mathrm{Na}(s) + \mathrm{Cl}_2(g) \rightarrow 2\ \mathrm{NaCl}(s)$$? (Molar masses: Na = 22.99 g/mol, $$\mathrm{Cl}_2 = 70.90 g/$$mol)

Accepted Answer

$$\mathrm{Cl}_2$$

Question 5

A chemical reaction produced 87.4 g of copper, but the theoretical yield was 101.7 g. What is the percent yield?

Accepted Answer

$$\frac{87.4\ \mathrm{g}}{101.7\ \mathrm{g}} 	imes 100\% = 85.9\%$$

Question 6

Which statement about the limiting reactant is correct?

Accepted Answer

The limiting reactant is the reactant that is completely consumed in a chemical reaction.

Question 7

Which equation correctly represents the calculation of percent yield?

Accepted Answer

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

Question 8

Which of the following reactions is exothermic?

Accepted Answer

$$\mathrm{CH}_4(g) + 2\ \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + 2\ \mathrm{H}_2\mathrm{O}(g)\ \Delta H_{rxn} = -802.3\ \mathrm{kJ}$$

Question 9

A propane tank contains $$1.18 	imes 10^4$ g of $$\mathrm{C}_3\mathrm{H}_8$$. How much heat is released upon complete combustion? (Molar mass $$\mathrm{C}_3\mathrm{H}_8$$ = 44.11 g/mol, $$\Delta H_{rxn} = -2044$$ kJ/mol)

Accepted Answer

$$1.18 	imes 10^4$\ \mathrm{g}\ \mathrm{C}_3\mathrm{H}_8 	imes \frac{1\ \mathrm{mol}\ \mathrm{C}_3\mathrm{H}_8}{44.11\ \mathrm{g}\ \mathrm{C}_3\mathrm{H}_8} 	imes \frac{-2044\ \mathrm{kJ}}{1\ \mathrm{mol}\ \mathrm{C}_3\mathrm{H}_8} = -5.47 	imes 10^5$\ \mathrm{kJ}$$

Question 10

Which statement about enthalpy ($$\Delta H_{rxn}) is $$correct?

Accepted Answer

A negative $$\Delta H_{rxn}$$ means the reaction releases heat to the surroundings.

Question 11

In 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 9 moles of $$\mathrm{H}_2$$ and excess $$\mathrm{N}_2$$?

Accepted Answer

6 moles

Question 12

Which of the following is NOT a reason why actual yield is usually less than theoretical yield?

Accepted Answer

The limiting reactant is always in excess.

Question 13

If 155 g of $$\mathrm{NH}_3$$ reacts completely according to $$4\ \mathrm{NH}_3(g) + 5\ \mathrm{O}_2(g) \rightarrow 4\ \mathrm{NO}(g) + 6\ \mathrm{H}_2\mathrm{O}$$ ($$\Delta H_{rxn} = -906 kJ$$), what is the heat released? (Molar mass $$\mathrm{NH}_3 = 17.03 g/$$mol)

Accepted Answer

$$155\ \mathrm{g}\ \mathrm{NH}_3 	imes \frac{1\ \mathrm{mol}\ \mathrm{NH}_3}{17.03\ \mathrm{g}\ \mathrm{NH}_3} 	imes \frac{-906\ \mathrm{kJ}}{4\ \mathrm{mol}\ \mathrm{NH}_3} = -2060\ \mathrm{kJ}$$

Question 14

Which of the following is a correct example of a mass-to-mass conversion in stoichiometry?

Accepted Answer

$$	ext{mass A} ightarrow 	ext{moles A} ightarrow 	ext{moles B} ightarrow 	ext{mass B}$$

Question 15

Which scenario best illustrates the concept of a limiting reactant?

Accepted Answer

You have enough flour for 15 pancakes, enough eggs for 25 pancakes, and enough baking powder for 40 pancakes. You can only make 15 pancakes.

Question 16

Which of the following statements about oxygenated fuels is correct?

Accepted Answer

Ethanol is now used as a substitute for MTBE to increase oxygen content in motor fuel.

Quantities in Chemical Reactions: Stoichiometry, Limiting Reactants, and Enthalpy

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