Q: A 0.50 mol sample of $$O_2$$ gas is contained in a 10.0 L vessel at 300 K. What is the pressure of the gas? (Use $$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

$$P = \dfrac{nRT}{V} = \dfrac{0.50 \times 0.0821 \times 300}{10.0} = 1.23\ \mathrm{atm}$$

Question 1

Which statement best describes the difference between a compound and a mixture?

Accepted Answer

A compound consists of two or more elements chemically bonded in fixed ratios, while a mixture contains substances physically combined in variable proportions.

Question 2

Which of the following electron configurations represents a neutral atom of sulfur ($$Z = 16$$)?

Accepted Answer

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

Question 3

A student analyzes a sample and determines it contains 12 protons, 12 neutrons, and 10 electrons. What is the identity and charge of the species?

Accepted Answer

Magnesium ion, $$Mg^{2+}$$

Question 4

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 large amounts of energy to break.

Question 5

Which molecule has a bent geometry according to VSEPR theory?

Accepted Answer

Water ($$H_2O)$$

Question 6

A 0.50 mol sample of $$O_2$$ gas is contained in a 10.0 L vessel at 300 K. What is the pressure of the gas? (Use $$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$P = \dfrac{nRT}{V} = \dfrac{0.50 	imes 0.0821 	imes 300}{10.0} = 1.23\ \mathrm{atm}$$

Question 7

Which of the following is an example of a physical change?

Accepted Answer

Boiling water to produce steam

Question 8

Which statement about the periodic trends of atomic radius is correct?

Accepted Answer

Atomic radius decreases across a period from left to right due to increasing nuclear charge.

Question 9

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

Accepted Answer

It lowers the activation energy, increasing the reaction rate without being consumed.

Question 10

A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 500 mL of solution. What is the molarity of the solution? ($$M = \dfrac{	ext{moles solute}}{	ext{liters solution}}$$, molar mass NaCl = 58.44 g/mol)

Accepted Answer

$$M = \dfrac{10.0\ \mathrm{g}}{58.44\ \mathrm{g/mol}} \div 0.500\ \mathrm{L} = 0.342\ \mathrm{M}$$

Question 11

Which of the following best describes the process of entropy ($$S) $$change in melting ice?

Accepted Answer

Entropy increases because the molecules become more disordered as ice melts to liquid water.

Question 12

Which of the following is the correct balanced equation for the combustion of methane ($$CH_4) in $$oxygen?

Accepted Answer

$$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$

Question 13

Which of the following statements about colligative properties is correct?

Accepted Answer

Colligative properties depend on the number of solute particles, not their identity.

Question 14

A reaction has a rate law: $$	ext{rate} = k[A]^2[B]. If $$the concentration of $$A is $$doubled and $$B is $$tripled, by what factor does the rate increase?

Accepted Answer

The rate increases by a factor of $$2^2$$ 	imes 3 = 12$$

Question 15

Which of the following is true about the relationship between pressure and volume for an ideal gas at constant temperature?

Accepted Answer

Pressure and volume are inversely proportional: $$P_1V_1 = P_2V_2$$

Question 16

Which of the following best describes the concept of activation energy in a chemical reaction?

Accepted Answer

It is the minimum energy required for reactants to form products.

Question 17

Which of the following is a correct statement about acids and bases according to the Brønsted-Lowry definition?

Accepted Answer

An acid is a proton donor and a base is a proton acceptor.

Question 18

Which of the following is the correct expression for Gibbs free energy change ($$\Delta G$$)?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 19

A radioactive isotope has a half-life of 5 years. If you start with 80 g, how much remains after 15 years?

Accepted Answer

After 3 half-lives ($$15/5$$), $$80 	imes (1/2)^3$ = 10 g $$remains.

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