Q: Calculate the percent composition by mass of oxygen in $$CO_2. ($$Atomic masses: C = 12.01 g/mol, O = 16.00 g/mol)

$$\frac{32.00}{44.01} \times 100\% = 72.7\%$$

Q: A sample contains $$6.170$$ mol of $$H_2O. $$How many hydrogen atoms are present in the sample?

$$6.170 \times 2 \times 6.022 \times 10$$^{23}$$ = 7.43 \times 10$$^{24}$$ atoms

Q: What is the molecular weight of $$C_2H_6O ($$ethanol)? (Atomic masses: C = 12.01 g/mol, H = 1.008 g/mol, O = 15.999 g/mol)

$$2 \times 12.01 + 6 \times 1.008 + 1 \times 15.999 = 46.069 g/$$mol

Q: A reaction produces 0.23 mol $$H_2$$ when 0.30 mol Zn reacts with 0.52 mol HCl. What is the percent yield if the theoretical yield is 0.26 mol $$H_2$$?

$$\frac{0.23}{0.26} \times 100\% = 88.5\%$$

Q: How many molecules are present in 0.445 mol of $$C_4H_8$$?

$$0.445 \times 6.022 \times 10$$^{23}$$ = 2.68 \times 10$$^{23}$$ molecules

Question 1

Which of the following is NOT considered evidence of a chemical reaction?

Accepted Answer

Melting of ice

Question 2

According to the Law of Mass Conservation, which statement is true for a balanced chemical equation?

Accepted Answer

The total number of atoms of each element is the same on both sides of the equation.

Question 3

What is the balanced chemical equation for the combustion of methane ($$CH_4) in $$oxygen?

Accepted Answer

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

Question 4

Which type of reaction is represented by the following equation: $$2 H_2O_2 (aq) \rightarrow 2 H_2O (l) + O_2$ (g)$$?

Accepted Answer

Decomposition reaction

Question 5

A student mixes 0.30 mol Zn with 0.52 mol HCl according to the reaction $$Zn + 2 HCl \rightarrow $$ZnCl_2$$ + H_2$. What is the limiting reactant?

Accepted Answer

Hydrochloric acid (HCl)

Question 6

Calculate the percent composition by mass of oxygen in $$CO_2. ($$Atomic masses: C = 12.01 g/mol, O = 16.00 g/mol)

Accepted Answer

$$\frac{32.00}{44.01} 	imes 100\% = 72.7\%$$

Question 7

What is the empirical formula for a compound containing 2 mol of C and 3 mol of H?

Accepted Answer

$$C_2H_3$$

Question 8

If you have 4.24 moles of $$H_2$$, how many moles of $$N_2$$ are needed to completely react according to $$N_2 + 3$$ $$H_2$$ \rightarrow 2 $$NH_3$$?

Accepted Answer

$$1.41$$ mol

Question 9

Which of the following is a double displacement reaction?

Accepted Answer

$$Ba(NO_3$)_2 (aq) + $$FeSO_4$$ (aq) \rightarrow $$BaSO_4$$ (s) + Fe(NO_3$)_2 (aq)$$

Question 10

A sample contains $$6.170$$ mol of $$H_2O. $$How many hydrogen atoms are present in the sample?

Accepted Answer

$$6.170 	imes 2 	imes 6.022 	imes 10$$^{23}$$ = 7.43 	imes 10$$^{24}$$ atoms

Question 11

Which of the following best describes the purpose of stoichiometry in chemical reactions?

Accepted Answer

To determine the quantitative relationship between reactants and products using their mole ratios

Question 12

What is the molecular weight of $$C_2H_6O ($$ethanol)? (Atomic masses: C = 12.01 g/mol, H = 1.008 g/mol, O = 15.999 g/mol)

Accepted Answer

$$2 	imes 12.01 + 6 	imes 1.008 + 1 	imes 15.999 = 46.069 g/$$mol

Question 13

A reaction produces 0.23 mol $$H_2$$ when 0.30 mol Zn reacts with 0.52 mol HCl. What is the percent yield if the theoretical yield is 0.26 mol $$H_2$$?

Accepted Answer

$$\frac{0.23}{0.26} 	imes 100\% = 88.5\%$$

Question 14

Which of the following outcomes does NOT typically result from a chemical reaction?

Accepted Answer

Decrease in entropy

Question 15

How many molecules are present in 0.445 mol of $$C_4H_8$$?

Accepted Answer

$$0.445 	imes 6.022 	imes 10$$^{23}$$ = 2.68 	imes 10$$^{23}$$ molecules

Question 16

Which step should be performed first when balancing a chemical equation?

Accepted Answer

Write the correct formulas for the reactants and products

Question 17

In the reaction $$Fe_2O_3 + 3 CO \rightarrow 2 Fe + 3 CO_2$, how many kg of Fe can be produced from 1.00 kg of Fe_2O_3$? (Molar mass Fe_2O_3 = 159.7$ g/mol, Fe = 55.85$ g/mol)

Accepted Answer

$$1.00 	ext{ kg } 	imes \frac{1000 	ext{ g}}{1 	ext{ kg}} 	imes \frac{2 	imes 55.85 	ext{ g Fe}}{159.7 	ext{ g } Fe_2O_3} = 0.70 	ext{ kg Fe}$$

Fundamentals of Chemical Reactions and Stoichiometry

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