Q: Given the actual yield is 11 pancakes and the theoretical yield is 15 pancakes, what is the percent yield?

$$\frac{11}{15} \times 100\% = 73\%$$

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

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

Q: If a chemical reaction produces 108 g NaCl as the theoretical yield and the actual yield is 86.4 g, what is the percent yield?

$$\frac{86.4}{108} \times 100\% = 80\%$$

Question 1

Which of the following best describes the greenhouse effect as illustrated in the study materials?

Accepted Answer

Greenhouse gases allow sunlight to enter the atmosphere but trap heat radiated from Earth's surface.

Question 2

The combustion of octane, a component of gasoline, produces which two main products?

Accepted Answer

Water and carbon dioxide

Question 3

If the balanced equation for the combustion of octane is $$2 \mathrm{C}_8\mathrm{H}_{18} + 25 \mathrm{O}_2 \rightarrow 16 \mathrm{CO}_2 + 18 \mathrm{H}_2\mathrm{O}$$, how many moles of $$\mathrm{CO}_2$$ are produced for every 2 moles of octane burned?

Accepted Answer

16 moles

Question 4

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

Accepted Answer

20 pancakes

Question 5

In the reaction $$N_2 + 3H_2$$ \rightarrow 2NH_3$$, if you start with 3 mol of N_2$ and excess H_2$, how many moles of NH_3$ can be produced?

Accepted Answer

6 moles

Question 6

Which term describes the reactant that is completely consumed in a chemical reaction, limiting the amount of product formed?

Accepted Answer

Limiting reactant

Question 7

If you have 3 cups of flour, 10 eggs, and 4 tsp baking powder, and the recipe allows for 15 pancakes with the flour, 25 with the eggs, and 40 with the baking powder, what is the limiting reactant?

Accepted Answer

Flour

Question 8

Given the actual yield is 11 pancakes and the theoretical yield is 15 pancakes, what is the percent yield?

Accepted Answer

$$\frac{11}{15} 	imes 100\% = 73\%$$

Question 9

In a chemical reaction, the theoretical yield is always:

Accepted Answer

Equal to or greater than the actual yield

Question 10

For the reaction $$\mathrm{Ti} + 2\mathrm{Cl}_2 \rightarrow \mathrm{TiCl}_4$$, if you start with 1.8 mol Ti and 3.2 mol Cl$$_2$$, what is the limiting reactant?

Accepted Answer

Cl$$_2$$

Question 11

For the same reaction above, what is the theoretical yield of TiCl$$_4$$?

Accepted Answer

1.6 mol

Question 12

Which equation correctly represents the calculation for percent yield?

Accepted Answer

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

Question 13

If a chemical reaction produces 108 g NaCl as the theoretical yield and the actual yield is 86.4 g, what is the percent yield?

Accepted Answer

$$\frac{86.4}{108} 	imes 100\% = 80\%$$

Question 14

Why is the actual yield almost always less than the theoretical yield in a chemical reaction?

Accepted Answer

Because some product does not form or is lost during the reaction.

Question 15

In industrial applications, why is the more costly reactant often chosen as the limiting reactant?

Accepted Answer

To minimize waste and cost.

Question 16

Which of the following is NOT a learning objective for Chapter 8?

Accepted Answer

Memorize the atomic structure of all elements.

Question 17

A balanced chemical equation provides which of the following?

Accepted Answer

Quantitative relationships between reactants and products.

Question 18

If the world burns the fossil fuel equivalent of 1.0 × 10$$^{12} kg of $$octane per year, and the balanced equation is $$2 \mathrm{C}_8\mathrm{H}_{18} + 25 \mathrm{O}_2 \rightarrow 16 \mathrm{CO}_2 + 18 \mathrm{H}_2\mathrm{O}$$, how many kg of $$\mathrm{CO}_2$$ are produced per year? (Molar mass of octane = 114 g/mol, $$\mathrm{CO}_2 = 44 g/$$mol)

Accepted Answer

6.2 × 10$$^{12} kg$$

Question 19

If the atmosphere currently contains 3.0 × 10$$^{12} kg of$$ $$\mathrm{CO}_2$$, and world fossil fuel combustion produces 6.2 × 10$$^{12} kg of$$ $$\mathrm{CO}_2$$ per year, how long will it take to double the atmospheric $$\mathrm{CO}_2$$?

Accepted Answer

0.5 years

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

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