Question 1

Which of the following best describes the quantum mechanical model of the atom as it relates to the electronic structure of atoms?

Accepted Answer

Electrons are found in defined energy levels, but their exact position and momentum cannot be simultaneously known due to the Heisenberg uncertainty principle.

Question 2

A student mixes 50.0 mL of 1.0 M HCl with 50.0 mL of 1.0 M NaOH in a coffee-cup calorimeter. The temperature of the solution rises by 6.0 °C. If the specific heat capacity of the solution is $$4.18 \ \mathrm{J} \cdot \mathrm{g}^{-1} \cdot \mathrm{K}^{-1}$$ and the density is $$1.00 \ \mathrm{g} \cdot \mathrm{mL}^{-1}$$, what is the enthalpy change ($$\Delta H) $$for the neutralization reaction per mole of water formed?

Accepted Answer

$$-57 \ \mathrm{kJ} \cdot \mathrm{mol}^{-1}$$

Question 3

Which of the following statements about covalent bonding is correct?

Accepted Answer

Covalent bonds are formed when two atoms share one or more pairs of electrons.

Question 4

Which of the following best explains why water has a higher boiling point than methane ($$\mathrm{CH}_4$$)?

Accepted Answer

Water molecules form hydrogen bonds, which are stronger than the London dispersion forces present in methane.

Question 5

A sample of gas occupies $$2.50 \ \mathrm{L} at$$ $$1.00 \ \mathrm{atm}$$ and $$25.0^\circ \mathrm{C}. $$What will be its volume at $$0.500 \ \mathrm{atm}$$ and $$50.0^\circ \mathrm{C}$$, assuming ideal gas behavior?

Accepted Answer

$$5.46 \ \mathrm{L}$$

Question 6

Which of the following is the correct electron configuration for a ground-state sulfur atom ($$Z=16$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^4$$

Question 7

Which of the following best describes the process of entropy change ($$\Delta S) $$when ice melts at $$0^\circ \mathrm{C}$$?

Accepted Answer

$$\Delta S is $$positive because the system becomes more disordered as solid turns to liquid.

Question 8

A reaction has $$\Delta H = +40 \ \mathrm{kJ} \cdot \mathrm{mol}^{-1}$$ and $$\Delta S = +100 \ \mathrm{J} \cdot \mathrm{mol}^{-1} \cdot \mathrm{K}^{-1}. At $$what temperature (in $$\mathrm{K}) $$does the reaction become spontaneous?

Accepted Answer

$$400 \ \mathrm{K}$$

Question 9

Which of the following is a correct statement about the first law of thermodynamics?

Accepted Answer

The total energy of an isolated system is constant; energy can be transferred or transformed but not created or destroyed.

Question 10

Which of the following best explains why ionic compounds tend to have high melting points?

Accepted Answer

Strong electrostatic forces between oppositely charged ions require a large amount of energy to break.

Question 11

A 0.500 mol sample of an ideal gas is confined in a $$10.0 \ \mathrm{L}$$ container at $$27.0^\circ \mathrm{C}. $$What is the pressure of the gas? ($$R = 0.0821 \ \mathrm{L} \cdot \mathrm{atm} \cdot \mathrm{mol}^{-1} \cdot \mathrm{K}^{-1})$$

Accepted Answer

$$1.22 \ \mathrm{atm}$$

Question 12

Which of the following is the best explanation for the trend in atomic radius across a period in the periodic table?

Accepted Answer

Atomic radius decreases across a period due to increasing nuclear charge, which pulls electrons closer to the nucleus.

Question 13

Which of the following is the correct balanced equation for the combustion of propane ($$\mathrm{C}_3\mathrm{H}_8) in $$oxygen?

Accepted Answer

$$\mathrm{C}_3\mathrm{H}_8 + 5\ \mathrm{O}_2 \rightarrow 3\ \mathrm{CO}_2 + 4\ \mathrm{H}_2\mathrm{O}$$

Question 14

Which of the following best describes the role of a catalyst in a chemical reaction?

Accepted Answer

A catalyst lowers the activation energy, increasing the rate of the reaction without being consumed.

Question 15

A solution is prepared by dissolving $$10.0 \ \mathrm{g} of $$NaCl in enough water to make $$500.0 \ \mathrm{mL} of $$solution. What is the molarity of the solution? (Molar mass of NaCl = $$58.44 \ \mathrm{g} \cdot \mathrm{mol}^{-1})$$

Accepted Answer

$$0.342 \ \mathrm{M}$$

Question 16

Which of the following is the correct Lewis structure for carbon dioxide ($$\mathrm{CO}_2$$)?

Accepted Answer

O=C=O, with each oxygen atom having two lone pairs.

Question 17

Which of the following best explains why ice floats on liquid water?

Accepted Answer

Ice is less dense than liquid water due to its open hexagonal structure formed by hydrogen bonding.

Question 18

Which of the following is the correct expression for the equilibrium constant ($$K_c) $$for the reaction $$\mathrm{N}_2(g) + 3\ \mathrm{H}_2(g) \rightleftharpoons 2\ \mathrm{NH}_3(g)$$?

Accepted Answer

$$K_c = \dfrac{[\mathrm{NH}_3]^2}{[\mathrm{N}_2][\mathrm{H}_2]^3}$$

Chemistry 31E, Fall 2025: Course Calendar Overview

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