Q: What is the mass of 0.25 moles of methane ($$CH_4$$)? (Atomic masses: C = 12.01 g/mol, H = 1.008 g/mol)

$$0.25 \times (12.01 + 4 \times 1.008) = 4.505 g$$

Q: A sample contains 2.00 mol He, 3.00 mol $$H_2$$, and 1.00 mol $$CH_4. $$How many total atoms are present?

$$2.00 \times 6.022 \times 10$$^{23}$$ + 3.00 \times 2 \times 6.022 \times 10$$^{23}$$ + 1.00 \times 5 \times 6.022 \times 10$$^{23}$$ = 3.01 \times 10$$^{24}$$ atoms

Q: How many nitrogen atoms are present in 4.72 g of magnesium nitrate, $$Mg(NO_3$)_2$$? (Molar mass $$Mg(NO_3$)_2 = 148.32 g/$$mol)

$$3.83 \times 10$$^{22}$$ N atoms

Q: How many water molecules are present in a 100.0 g sample of water? (Molar mass $$H_2O = 18.02 g/$$mol)

$$3.34 \times 10$$^{24}$$ molecules

Q: What is the percent yield if 10.0 g of $$N_2$$ and 2.50 g of $$H_2$$ react to produce 12.2 g of $$NH_3$$? (Molar mass $$N_2 = 28.02$ g/mol, H_2$ = 2.016 g/$$mol, $$NH_3 = 17.03$ g/mol)

$$\frac{12.2}{14.2} \times 100\% = 86\%$$

Q: How many grams of $$CO_2$$ are produced when 2.50 g of $$C_6H_{12}O_6$ reacts completely? (Molar mass C_6H$$_{12}$$O_6 = 180.16$ g/mol, CO_2$ = 44.01 g/$$mol, reaction: $$C_6H_{12}O_6$ + 6 O_2$ \rightarrow 6 CO_2$ + 6 H_2O)$$

$$2.50 \text{ g } \times \frac{1 \text{ mol } C_6H_{12}O_6$}{180.16 \text{ g}} \times \frac{6 \text{ mol } CO_2$}{1 \text{ mol } C_6H_{12}O_6$} \times 44.01 \text{ g } CO_2$ = 3.67 \text{ g }$$

Question 1

Which of the following best describes a decomposition reaction?

Accepted Answer

A reaction where a single reactant breaks down into two or more products.

Question 2

What is the mass of 0.25 moles of methane ($$CH_4$$)? (Atomic masses: C = 12.01 g/mol, H = 1.008 g/mol)

Accepted Answer

$$0.25 	imes (12.01 + 4 	imes 1.008) = 4.505 g$$

Question 3

A sample contains 2.00 mol He, 3.00 mol $$H_2$$, and 1.00 mol $$CH_4. $$How many total atoms are present?

Accepted Answer

$$2.00 	imes 6.022 	imes 10$$^{23}$$ + 3.00 	imes 2 	imes 6.022 	imes 10$$^{23}$$ + 1.00 	imes 5 	imes 6.022 	imes 10$$^{23}$$ = 3.01 	imes 10$$^{24}$$ atoms

Question 4

Which of the following is the correct balanced equation for the combustion of ethanol ($$C_2H_5OH$$)?

Accepted Answer

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

Question 5

How many nitrogen atoms are present in 4.72 g of magnesium nitrate, $$Mg(NO_3$)_2$$? (Molar mass $$Mg(NO_3$)_2 = 148.32 g/$$mol)

Accepted Answer

$$3.83 	imes 10$$^{22}$$ N atoms

Question 6

A compound is found to be 84.4% carbon and 15.6% hydrogen by mass. What is its empirical formula?

Accepted Answer

$$CH_2$$

Question 7

If the compound in the previous question has a molecular weight of 14 g/mol, what is its molecular formula?

Accepted Answer

$$CH_2$$

Question 8

Which formula is consistent with a compound found to be comprised of 36.6% Cr, 12.7% C, and oxygen as the remainder?

Accepted Answer

$$Cr_2$$($$CO_3)_3$

Question 9

How many water molecules are present in a 100.0 g sample of water? (Molar mass $$H_2O = 18.02 g/$$mol)

Accepted Answer

$$3.34 	imes 10$$^{24}$$ molecules

Question 10

Which statement about Avogadro’s number is correct?

Accepted Answer

It is the number of molecules in 1 mole of any substance.

Question 11

What is the percent yield if 10.0 g of $$N_2$$ and 2.50 g of $$H_2$$ react to produce 12.2 g of $$NH_3$$? (Molar mass $$N_2 = 28.02$ g/mol, H_2$ = 2.016 g/$$mol, $$NH_3 = 17.03$ g/mol)

Accepted Answer

$$\frac{12.2}{14.2} 	imes 100\% = 86\%$$

Question 12

In the reaction $$N_2 (g) + 3$$ $$H_2 (g$$) \rightarrow 2 $$NH_3 (g$$)$$, if 10.0 g of N_2$ and 2.50 g of H_2$ are mixed, which is the limiting reactant?

Accepted Answer

$$H_2$$

Question 13

How many grams of $$CO_2$$ are produced when 2.50 g of $$C_6H_{12}O_6$ reacts completely? (Molar mass C_6H$$_{12}$$O_6 = 180.16$ g/mol, CO_2$ = 44.01 g/$$mol, reaction: $$C_6H_{12}O_6$ + 6 O_2$ \rightarrow 6 CO_2$ + 6 H_2O)$$

Accepted Answer

$$2.50 	ext{ g } 	imes \frac{1 	ext{ mol } C_6H_{12}O_6$}{180.16 	ext{ g}} 	imes \frac{6 	ext{ mol } CO_2$}{1 	ext{ mol } C_6H_{12}O_6$} 	imes 44.01 	ext{ g } CO_2$ = 3.67 	ext{ g }$$

Question 14

Which of the following is a combination reaction?

Accepted Answer

$$2 Na (s) + Cl_2$ (g) \rightarrow 2 NaCl (s)$$

Question 15

If 2.0 g of $$H_2$$ reacts with an unknown amount of $$O_2 to $$produce 76.0 g of $$H_2O$$, how much $$H_2$$ remains after the reaction proceeds to 100% yield? ($$2 H_2$ + O_2$ \rightarrow 2 H_2O$$, molar mass $$H_2 = 2.016$ g/mol, H_2O = 18.02$ g/mol)

Accepted Answer

1.0 g $$H_2$$ remains

Question 16

Which of the following statements about formula weight and molecular weight is correct?

Accepted Answer

Formula weight is used for ionic compounds, while molecular weight is used for covalent compounds.

Question 17

How many moles of $$H_2O$$ are present in a 100.0 g sample? (Molar mass $$H_2O = 18.02 g/$$mol)

Accepted Answer

$$5.55$$ moles

Question 18

Which of the following is the correct conversion factor to go from grams to atoms for any element?

Accepted Answer

$$\frac{1 	ext{ mol}}{	ext{molar mass in g}} 	imes \frac{6.022 	imes 10$$^{23}$$ 	ext{ atoms}}{1 	ext{ mol}}$$

Chapter 3: Chemical Equations, Stoichiometry, and Chemical Quantities

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