Q: Which of the following is the correct formula for calculating percent yield?

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

Question 1

Which of the following best describes the greenhouse effect?

Accepted Answer

The process by which greenhouse gases trap heat in Earth's atmosphere, warming the planet.

Question 2

Why are scientists concerned about the increase in atmospheric carbon dioxide ($$\mathrm{CO_2$}$$)?

Accepted Answer

Because increased $$\mathrm{CO_2$}$$ enhances the greenhouse effect, leading to global warming.

Question 3

Which of the following is a balanced chemical equation for the combustion of methane?

Accepted Answer

$$\mathrm{CH_4$(g) + 2\ O_2$(g) \rightarrow CO_2$(g) + 2\ H_2O(g)}$$

Question 4

In the reaction $$\mathrm{2\ Mg(s) + O_2$(g) \rightarrow 2\ MgO(s)}$$, if you start with 42.5 g of Mg and 33.8 g of $$\mathrm{O_2$}$$, what is the limiting reactant?

Accepted Answer

Mg

Question 5

Which quantity must always be the same on both sides of a balanced chemical equation?

Accepted Answer

The number of atoms of each kind

Question 6

A reaction has a theoretical yield of 45.8 g. When the reaction is carried out, 37.2 g of the product is obtained. What is the percent yield?

Accepted Answer

$$81.2\%$$

Question 7

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

Accepted Answer

The reactant that is completely consumed and limits the amount of product formed.

Question 8

Consider the reaction: $$\mathrm{2\ C_4H_{10}(g) + 13\ O_2$(g) \rightarrow 8\ CO_2$(g) + 10\ H_2O(g)}. $$How many moles of $$\mathrm{CO_2$}$$ are produced from 5.0 moles of $$\mathrm{C_4H_{10}} ($$assuming excess $$\mathrm{O_2$}$$)?

Accepted Answer

20 moles

Question 9

Which of the following is the correct balanced equation for the reaction of sodium with water?

Accepted Answer

$$\mathrm{2\ Na(s) + 2\ H_2O(l) \rightarrow 2\ NaOH(aq) + H_2$(g)}$$

Question 10

A chemist burns 4.0 $$	imes$$ $$10^{15} g of $$octane ($$\mathrm{C_8H_{18}}). $$How much $$\mathrm{CO_2$} (in $$grams) is produced? (Molar masses: $$\mathrm{C_8H_{18}} = 114.22 g/$$mol, $$\mathrm{CO_2$} = 44.01 g/$$mol)

Accepted Answer

$$1.2 	imes 10$$^{16}$$ g

Question 11

Which of the following is the correct formula for calculating percent yield?

Accepted Answer

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

Question 12

Which of the following is a combustion reaction?

Accepted Answer

$$\mathrm{C_2H_5OH(l) + 3\ O_2$(g) \rightarrow 2\ CO_2$(g) + 3\ H_2O(g)}$$

Question 13

Which of the following statements about balancing chemical equations is correct?

Accepted Answer

You can only change the coefficients, not the subscripts, to balance the equation.

Question 14

In the reaction $$\mathrm{N_2$(g) + 3\ H_2$(g) \rightarrow 2\ NH_3$(g)}$$, if you start with 5.0 mol $$\mathrm{N_2$}$$ and 12.0 mol $$\mathrm{H_2$}$$, what is the limiting reactant?

Accepted Answer

$$\mathrm{H_2$}$$

Question 15

Which of the following is the correct balanced equation for the reaction of chlorine gas with iron to form iron(III) chloride?

Accepted Answer

$$\mathrm{2\ Fe(s) + 3\ Cl_2$(g) \rightarrow 2\ $$FeCl_3$$(s)}$$

Question 16

A student reacts 37.8 g of $$\mathrm{CO_2$}$$ with excess water in photosynthesis. What mass of glucose ($$\mathrm{C_6H_{12}O_6$}$$, molar mass = 180.2 g/mol) can be produced? ($$\mathrm{6\ CO_2$ + 6\ H_2O \rightarrow C_6H_{12}O_6$ + 6\ O_2$}$$, $$\mathrm{CO_2$}$$ molar mass = 44.01 g/mol)

Accepted Answer

25.8 g

Question 17

Which of the following best describes the products of a complete combustion reaction of a hydrocarbon?

Accepted Answer

Carbon dioxide and water

Question 18

Which of the following is the correct balanced equation for the reaction of hydrogen gas with bromine gas?

Accepted Answer

$$\mathrm{H_2$(g) + Br_2$(g) \rightarrow 2\ HBr(g)}$$

Chapter 4: Chemical Reactions and Chemical Quantities

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