Q: Calculate the percent composition of carbon in glucose ($$\mathrm{C_6H_{12}O_6$}).$$

$$\mathrm{\%C = \frac{6 \times 12.0}{180.0} \times 100 = 40.0\%}$$

Q: How many molecules are present in 2.00 moles of water ($$\mathrm{H_2O}$$)?

$$\mathrm{2.00 \times 6.02 \times 10$$^{23}$$ = 1.20 \times 10$$^{24}$$}$$ molecules

Q: A sample contains 3 g of copper ($$\mathrm{Cu}). $$How many atoms of copper are present? (Atomic mass of Cu = 63.5 g/mol)

$$\mathrm{\frac{3\ g}{63.5\ g/mol} \times 6.02 \times 10$$^{23}$$ = 2.85 \times 10$$^{22}$$}$$ atoms

Q: In a reaction, 10.0 g of $$\mathrm{CH_4$} is $$combusted with excess $$\mathrm{O_2$}. $$How many grams of $$\mathrm{CO_2$}$$ are produced? ($$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$; molar mass $$\mathrm{CH_4$} = 16.0 g/$$mol, $$\mathrm{CO_2$} = 44.0 g/$$mol)

$$\mathrm{10.0\ g\ CH_4$ \times \frac{1\ mol\ CH_4$}{16.0\ g} \times \frac{1\ mol\ CO_2$}{1\ mol\ CH_4$} \times \frac{44.0\ g\ CO_2$}{1\ mol\ CO_2$} = 27.5\ g\ CO_2$}$$

Q: If the actual yield of a reaction is 15.0 g and the theoretical yield is 20.0 g, what is the percent yield?

$$\mathrm{\frac{15.0}{20.0} \times 100 = 75.0\%}$$

Question 1

Which of the following best describes the Law of Conservation of Mass as it applies to chemical equations?

Accepted Answer

The total mass of reactants must equal the total mass of products.

Question 2

Why do chemists balance chemical equations by changing coefficients rather than subscripts?

Accepted Answer

Changing subscripts creates new substances with different properties.

Question 3

Which of the following is the correct balanced equation for the combustion of propane ($$\mathrm{C_3H_8}$$)?

Accepted Answer

$$\mathrm{C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g)}$$

Question 4

A student heats $$\mathrm{$$CaCO_3$$(s)}$$ and collects the products. Which type of reaction is this and what are the products?

Accepted Answer

Decomposition reaction; $$\mathrm{$$CaCO_3$$(s) \rightarrow CaO(s) + CO_2$(g)}$$

Question 5

What is the formula weight (FW) of $$\mathrm{H_2SO_4} in $$amu?

Accepted Answer

$$\mathrm{FW = 98.1\ amu}$$

Question 6

Calculate the percent composition of carbon in glucose ($$\mathrm{C_6H_{12}O_6$}).$$

Accepted Answer

$$\mathrm{\%C = \frac{6 	imes 12.0}{180.0} 	imes 100 = 40.0\%}$$

Question 7

How many molecules are present in 2.00 moles of water ($$\mathrm{H_2O}$$)?

Accepted Answer

$$\mathrm{2.00 	imes 6.02 	imes 10$$^{23}$$ = 1.20 	imes 10$$^{24}$$}$$ molecules

Question 8

A sample contains 3 g of copper ($$\mathrm{Cu}). $$How many atoms of copper are present? (Atomic mass of Cu = 63.5 g/mol)

Accepted Answer

$$\mathrm{\frac{3\ g}{63.5\ g/mol} 	imes 6.02 	imes 10$$^{23}$$ = 2.85 	imes 10$$^{22}$$}$$ atoms

Question 9

Given the empirical formula $$\mathrm{CH}$$ and a molar mass of 78 g/mol, what is the molecular formula?

Accepted Answer

$$\mathrm{C_6H_6}$$

Question 10

A compound is found to contain 61.31% C, 5.14% H, 10.21% N, and 23.33% O by mass. What is its empirical formula?

Accepted Answer

$$\mathrm{C_7H_7NO_2}$$

Question 11

Which of the following statements about limiting reactants is correct?

Accepted Answer

The limiting reactant is the one that will be used up first in a reaction.

Question 12

In a reaction, 10.0 g of $$\mathrm{CH_4$} is $$combusted with excess $$\mathrm{O_2$}. $$How many grams of $$\mathrm{CO_2$}$$ are produced? ($$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$; molar mass $$\mathrm{CH_4$} = 16.0 g/$$mol, $$\mathrm{CO_2$} = 44.0 g/$$mol)

Accepted Answer

$$\mathrm{10.0\ g\ CH_4$ 	imes \frac{1\ mol\ CH_4$}{16.0\ g} 	imes \frac{1\ mol\ CO_2$}{1\ mol\ CH_4$} 	imes \frac{44.0\ g\ CO_2$}{1\ mol\ CO_2$} = 27.5\ g\ CO_2$}$$

Question 13

If the actual yield of a reaction is 15.0 g and the theoretical yield is 20.0 g, what is the percent yield?

Accepted Answer

$$\mathrm{\frac{15.0}{20.0} 	imes 100 = 75.0\%}$$

Question 14

Which of the following is a combination reaction?

Accepted Answer

$$\mathrm{N_2$(g) + 3H_2(g) \rightarrow 2NH_3(g)}$$

Question 15

During combustion analysis, how is the mass of hydrogen in a sample determined?

Accepted Answer

By measuring the mass of $$\mathrm{H_2O}$$ produced.

Question 16

Which of the following is the correct formula for calculating percent composition of an element in a compound?

Accepted Answer

$$\mathrm{\%\ Element = \frac{	ext{number of atoms} 	imes 	ext{atomic weight}}{	ext{formula weight}} 	imes 100}$$

Question 17

Which of the following best describes a combustion reaction?

Accepted Answer

A reaction in which a compound reacts rapidly with oxygen to produce a flame.

Chapter 3: Chemical Reactions and Reaction Stoichiometry – Study Notes

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드