Q: Which of the following equations correctly represents the calculation for percent yield?

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

Question 1

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

Accepted Answer

Greenhouse gases allow sunlight to enter the atmosphere but prevent heat from escaping, causing Earth's temperature to rise.

Question 2

Given the balanced equation for the combustion of octane: $$2\ \mathrm{C_8H_{18}}(l) + 25\ \mathrm{O_2$}(g) \rightarrow 16\ \mathrm{CO_2$}(g) + 18\ \mathrm{H_2O}(g)$$, 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 10 eggs and the pancake recipe requires 2 eggs for every 5 pancakes, how many pancakes can you make, assuming you have enough of the other ingredients?

Accepted Answer

25 pancakes

Question 4

Which of the following is the correct definition of the limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed in a chemical reaction, limiting the amount of product formed.

Question 5

A car burns $$5.0 	imes 10^2$ g of octane ($$\mathrm{C_8H_{18}}$$). Using the equation 2$$\ \mathrm{C_8H_{18}}(l) + 25\ \mathrm{$$O_2$$}(g) ightarrow 16\ \mathrm{$$CO_2$$}(g) + 18\ \mathrm{H_2O}(g)$$, what mass of $$\mathrm{$$CO_2$$}$$ is produced? (Molar masses: $$\mathrm{C_8H_{18}} = 114.3$$ g/mol, $$\mathrm{$$CO_2$$} = 44.01$$ g/mol)

Accepted Answer

$$1.5 	imes 10^3$ g

Question 6

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 6 moles of $$\mathrm{H_2$}$$ and excess $$\mathrm{N_2$}$$?

Accepted Answer

4 moles

Question 7

A reaction has a theoretical yield of 15 pancakes, but only 11 pancakes are actually made. What is the percent yield?

Accepted Answer

$$73\%$$

Question 8

Which of the following best describes stoichiometry?

Accepted Answer

The numerical relationship between chemical quantities in a balanced chemical equation.

Question 9

Given the reaction $$2\ \mathrm{Na}(s) + \mathrm{Cl_2$}(g) \rightarrow 2\ \mathrm{NaCl}(s)$$, if you start with 53.2 g Na and 65.8 g $$\mathrm{Cl_2$}$$, what is the limiting reactant? (Molar masses: Na = 22.99 g/mol, $$\mathrm{Cl_2$} = 70.90 g/$$mol)

Accepted Answer

$$\mathrm{Cl_2$}$$

Question 10

If the actual yield of $$\mathrm{NaCl} in $$the previous reaction is 86.4 g and the theoretical yield is 108 g, what is the percent yield?

Accepted Answer

$$80.0\%$$

Question 11

In a reaction, 11.5 g $$\mathrm{Cu_2O}$$ and 114.5 g C are reacted, producing 87.4 g Cu. If the theoretical yield is 101.7 g Cu, what is the percent yield?

Accepted Answer

$$85.9\%$$

Question 12

Which of the following is NOT a greenhouse gas?

Accepted Answer

Oxygen ($$\mathrm{O_2$})$$

Question 13

Why is the actual yield of a chemical reaction usually less than the theoretical yield?

Accepted Answer

Some product is lost or does not form during the reaction.

Question 14

If the world's annual fossil fuel consumption is $$9.0 	imes 10$$^{12}$$ kg of octane ($$\mathrm{C_8H_{18}}$$), how many moles of octane are consumed per year? (Molar mass of $$\mathrm{C_8H_{18}} = 114.3$$ g/mol)

Accepted Answer

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

Question 15

Which of the following equations correctly represents the calculation for percent yield?

Accepted Answer

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

Chapter 8: Quantities in Chemical Reactions – Stoichiometry, Limiting Reactants, and Yield

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