Q: How many molecules are present in 2 moles of water ($$\mathrm{H_2O}$$)?

$$1.20 \times 10$$^{24}$$ molecules

Q: A sample contains 3 g of copper ($$\mathrm{Cu}). $$How many atoms of copper are present? (Molar mass of Cu = 63.5 g/mol, Avogadro's number = $$6.02 \times 10$$^{23}$$)

$$2.85 \times 10$$^{22}$$ atoms

Q: Which equation correctly calculates the percent yield?

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

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 in a chemical reaction.

Question 2

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

Accepted Answer

Changing coefficients preserves the identity of the substances involved, while changing subscripts would create new substances.

Question 3

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

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 gas produced. What is the identity of the gas and the balanced equation for the reaction?

Accepted Answer

The gas is $$\mathrm{CO_2$}$$ and the equation is $$\mathrm{$$CaCO_3$$(s) \rightarrow CaO(s) + CO_2$(g)}$$

Question 5

Which of the following is a combination reaction?

Accepted Answer

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

Question 6

Calculate the formula weight of $$\mathrm{H_2SO_4}$$ using the atomic weights: H = 1.0 amu, S = 32.1 amu, O = 16.0 amu.

Accepted Answer

$$98.1$$ amu

Question 7

What is the percent composition of carbon in glucose ($$\mathrm{C_6H_{12}O_6$}$$)? (C = 12.0 amu, H = 1.0 amu, O = 16.0 amu)

Accepted Answer

$$40.0\%$$

Question 8

How many molecules are present in 2 moles of water ($$\mathrm{H_2O}$$)?

Accepted Answer

$$1.20 	imes 10$$^{24}$$ molecules

Question 9

A sample contains 3 g of copper ($$\mathrm{Cu}). $$How many atoms of copper are present? (Molar mass of Cu = 63.5 g/mol, Avogadro's number = $$6.02 	imes 10$$^{23}$$)

Accepted Answer

$$2.85 	imes 10$$^{22}$$ atoms

Question 10

Given the percent composition of para-aminobenzoic acid (PABA) as C: 61.31%, H: 5.14%, N: 10.21%, O: 23.33%, what is the empirical formula?

Accepted Answer

$$\mathrm{C_7H_7NO_2}$$

Question 11

A compound has an empirical formula of CH and a molar mass of 78 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C_6H_6}$$

Question 12

Which of the following statements about limiting reactants is correct?

Accepted Answer

The limiting reactant is the reactant that is completely consumed first, limiting the amount of product formed.

Question 13

If 2.6 g of $$\mathrm{C_6H_6}$$ reacts with excess $$\mathrm{O_2$} to $$produce 1.25 g of water, what is the percent yield of water? (Molar mass of $$\mathrm{C_6H_6} = 78.11 g/$$mol, Molar mass of $$\mathrm{H_2O} = 18.015 g/$$mol, 3 mol $$\mathrm{H_2O}$$ produced per 1 mol $$\mathrm{C_6H_6})$$

Accepted Answer

$$69.5\%$$

Question 14

Which equation correctly calculates the percent yield?

Accepted Answer

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

Question 15

Which of the following is NOT a type of reaction discussed in Chapter 3?

Accepted Answer

Precipitation reaction

Question 16

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

Accepted Answer

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

Question 17

Which of the following best describes a decomposition reaction?

Accepted Answer

A single reactant breaks down into two or more products.

Question 18

What is the molar mass of $$\mathrm{$$AgNO_3$$}$$? (Ag = 107.9 g/mol, N = 14.0 g/mol, O = 16.0 g/mol)

Accepted Answer

$$169.9 g/$$mol

Chapter 3: Chemical Reactions and Reaction Stoichiometry – Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards