Q: Which equation correctly expresses percent yield in a chemical reaction?

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

Q: If $$1.18 \times 10^4$\ \mathrm{g} of $$propane ($$\mathrm{C}_3\mathrm{H}_8) is $$combusted, how much heat is released? ($$\Delta H_{rxn} = -2044\ \mathrm{kJ}$$ per mole, molar mass $$44.11\ \mathrm{g/mol})$$

$$-5.47 \times 10^5$\ \mathrm{kJ}$$

Q: If the world burns $$9.0 \times 10$$^{12}$$\ \mathrm{kg} of $$octane per year, how many moles of octane are combusted annually? (Molar mass of octane = $$114.3\ \mathrm{g/mol})$$

$$7.87 \times 10$$^{13}$$ moles

Question 1

Which of the following best describes the role of greenhouse gases in Earth's atmosphere?

Accepted Answer

They allow sunlight to enter but prevent heat from escaping, leading to increased temperatures.

Question 2

Given the balanced chemical 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 5 moles of $$\mathrm{C}_8\mathrm{H}_{18}$$, assuming excess oxygen?

Accepted Answer

$$40$$ moles

Question 3

If you have 114.5 g of carbon and 11.5 g of $$\mathrm{Cu}_2\mathrm{O}$$, which is the limiting reactant in the reaction $$\mathrm{Cu}_2\mathrm{O}(s) + \mathrm{C}(s) \rightarrow 2\mathrm{Cu}(s) + \mathrm{CO}(g)$$?

Accepted Answer

$$\mathrm{Cu}_2\mathrm{O}$$

Question 4

Which equation correctly expresses percent yield in a chemical reaction?

Accepted Answer

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

Question 5

A chemical reaction has $$\Delta H_{rxn} = -802.3\ \mathrm{kJ}. $$What does this value indicate?

Accepted Answer

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

Question 6

How many grams of $$\mathrm{CO}_2$$ are produced from the complete combustion of $$100.0\ \mathrm{g} of $$octane ($$\mathrm{C}_8\mathrm{H}_{18}$$)? Use the molar mass $$114.3\ \mathrm{g/mol}$$ for octane and $$44.01\ \mathrm{g/mol}$$ for $$\mathrm{CO}_2. $$The balanced equation is $$2\mathrm{C}_8\mathrm{H}_{18} + 25\mathrm{O}_2 \rightarrow 16\mathrm{CO}_2 + 18\mathrm{H}_2\mathrm{O}.$$

Accepted Answer

$$308.0\ \mathrm{g}$$

Question 7

Which of the following statements about limiting reactants is correct?

Accepted Answer

The limiting reactant is the one that is completely consumed first, limiting the amount of product formed.

Question 8

A laboratory reaction produces $$86.4\ \mathrm{g} of$$ $$\mathrm{NaCl}$$, but the theoretical yield is $$108\ \mathrm{g}. $$What is the percent yield?

Accepted Answer

$$80.0\%$$

Question 9

Which of the following is a correct mole-to-mole conversion factor for the reaction $$3\mathrm{H}_2(g) + \mathrm{N}_2(g) \rightarrow 2\mathrm{NH}_3(g)$$?

Accepted Answer

$$\dfrac{2\ \mathrm{mol}\ \mathrm{NH}_3}{3\ \mathrm{mol}\ \mathrm{H}_2}$$

Question 10

If $$1.18 	imes 10^4$\ \mathrm{g} of $$propane ($$\mathrm{C}_3\mathrm{H}_8) is $$combusted, how much heat is released? ($$\Delta H_{rxn} = -2044\ \mathrm{kJ}$$ per mole, molar mass $$44.11\ \mathrm{g/mol})$$

Accepted Answer

$$-5.47 	imes 10^5$\ \mathrm{kJ}$$

Question 11

Which of the following reactions is endothermic?

Accepted Answer

$$\mathrm{N}_2(g) + \mathrm{O}_2(g) \rightarrow 2\mathrm{NO}(g)\ \Delta H_{rxn} = +182.6\ \mathrm{kJ}$$

Question 12

A recipe for pancakes requires 2 eggs for 5 pancakes. If you have 8 eggs and enough of all other ingredients, how many pancakes can you make?

Accepted Answer

20 pancakes

Question 13

Which of the following best explains why actual yield is usually less than theoretical yield in chemical reactions?

Accepted Answer

Some product is lost during the reaction or does not form due to side reactions.

Question 14

In the reaction $$\mathrm{Ti}(s) + 2\mathrm{Cl}_2(g) \rightarrow \mathrm{TiCl}_4(s)$$, if you start with $$1.8$$ mol $$\mathrm{Ti}$$ and $$3.2$$ mol $$\mathrm{Cl}_2$$, what is the theoretical yield of $$\mathrm{TiCl}_4 in $$moles?

Accepted Answer

$$1.6$$ mol

Question 15

Which of the following is NOT a greenhouse gas?

Accepted Answer

Oxygen ($$\mathrm{O}_2)$$

Question 16

If the world burns $$9.0 	imes 10$$^{12}$$\ \mathrm{kg} of $$octane per year, how many moles of octane are combusted annually? (Molar mass of octane = $$114.3\ \mathrm{g/mol})$$

Accepted Answer

$$7.87 	imes 10$$^{13}$$ moles

Question 17

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 18

Which of the following is the correct sequence for a mass-to-mass stoichiometry calculation?

Accepted Answer

Mass of reactant $$\rightarrow$$ moles of reactant $$\rightarrow$$ moles of product $$\rightarrow$$ mass of product

Stoichiometry and Energy in Chemical Reactions: Chapter 8 Study Notes

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