Q: Which of the following statements about Avogadro's number is correct?

Avogadro's number is $6.022 \times 10^{23}$ and represents the number of particles in 1 mole of a substance.

Q: Which of the following is the correct formula for calculating the enthalpy change ($\Delta H$) of a reaction using bond energies?

$\Delta H = \sum \text{(bond energies of bonds broken)} - \sum \text{(bond energies of bonds formed)}$

Question 1

Which of the following best describes a chemical change, and which real-world example illustrates it?

Accepted Answer

A change that alters the composition of matter, such as iron rusting.

Question 2

A sample of chlorine consists of two isotopes: $^{35}\mathrm{Cl}$ (75.77%, mass = 34.969 amu) and $^{37}\mathrm{Cl}$ (24.23%, mass = 36.966 amu). What is the atomic mass of chlorine?

Accepted Answer

$35.45\ \mathrm{amu}$

Question 3

Which of the following statements about Avogadro's number is correct?

Accepted Answer

Avogadro's number is $6.022 	imes 10^{23}$ and represents the number of particles in 1 mole of a substance.

Question 4

A 25.0 g sample of glucose ($\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$) is dissolved in enough water to make 0.500 L of solution. What is the molarity of the solution? (Molar mass of glucose = $180.16\ \mathrm{g/mol}$)

Accepted Answer

$0.278\ \mathrm{M}$

Question 5

Which of the following best explains why the atomic mass of an element is not a whole number?

Accepted Answer

Because the atomic mass is an average of the masses of all the isotopes, weighted by their natural abundance.

Question 6

A chemical reaction has a theoretical yield of 10.0 g, but only 7.5 g of product is actually obtained. What is the percent yield?

Accepted Answer

$75\%$

Question 7

Which of the following is a strong electrolyte in aqueous solution?

Accepted Answer

Sodium chloride ($\mathrm{NaCl}$)

Question 8

A 10.0 mL sample of 2.00 M HCl is diluted to a final volume of 100.0 mL. What is the final concentration?

Accepted Answer

$0.20\ \mathrm{M}$

Question 9

Which of the following best describes the difference between a sigma ($\sigma$) bond and a pi ($\pi$) bond?

Accepted Answer

A $\sigma$ bond is formed by the end-to-end overlap of orbitals along the internuclear axis, while a $\pi$ bond is formed by the side-to-side overlap of parallel p orbitals.

Question 10

Which of the following statements about the ideal gas law is correct?

Accepted Answer

The ideal gas law is $PV = nRT$, where $R = 0.08206\ \mathrm{L \cdot atm \cdot mol^{-1} \cdot K^{-1}}$.

Question 11

A gas mixture contains 2.0 mol of O$_2$ and 3.0 mol of N$_2$ at a total pressure of 5.0 atm. What is the partial pressure of O$_2$?

Accepted Answer

$2.0\ \mathrm{atm}$

Question 12

Which of the following best describes the concept of resonance in Lewis structures?

Accepted Answer

Resonance structures differ only by the movement of electrons, not atoms.

Question 13

Which of the following molecules is nonpolar, despite having polar bonds?

Accepted Answer

CO$_2$

Question 14

Which of the following is the correct electron configuration for the Fe$^{2+}$ ion?

Accepted Answer

$[\mathrm{Ar}]\ 3d^6$

Question 15

A sample of gas occupies 5.00 L at 1.00 atm and 300 K. What will be its volume at 2.00 atm and 300 K, assuming ideal behavior?

Accepted Answer

$2.50\ \mathrm{L}$

Question 16

Which of the following best describes the role of the oxidizing agent in a redox reaction?

Accepted Answer

The oxidizing agent is reduced and causes another substance to be oxidized.

Question 17

Which of the following is the correct formula for calculating the enthalpy change ($\Delta H$) of a reaction using bond energies?

Accepted Answer

$\Delta H = \sum 	ext{(bond energies of bonds broken)} - \sum 	ext{(bond energies of bonds formed)}$

Question 18

A 100.0 g sample of water is heated from 25.0 $^\circ$C to 75.0 $^\circ$C. If the specific heat capacity of water is $4.18\ \mathrm{J/g\cdot ^\circ C}$, how much heat is absorbed?

Accepted Answer

$20,900\ \mathrm{J}$

Question 19

Which of the following best describes the difference between electronic geometry and molecular geometry?

Accepted Answer

Electronic geometry considers all electron groups (bonding and lone pairs), while molecular geometry considers only the positions of atoms (bonds).

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