Q: A sample of an ideal gas occupies 10.0 L at 2.00 atm and 300 K. If the pressure is decreased to 1.00 atm and the temperature is increased to 400 K, what will be the new volume of the gas? Use the ideal gas law.

$$V_2$$ = $$V_1$$ \times \frac{$$P_1$$}{$$P_2$$} \times \frac{$$T_2$$}{$$T_1$$} = 10.0\,\text{L} \times \frac{2.00}{1.00} \times \frac{400}{300} = 26.7\,\text{L}$$

Question 1

A sample of an ideal gas occupies 10.0 L at 2.00 atm and 300 K. If the pressure is decreased to 1.00 atm and the temperature is increased to 400 K, what will be the new volume of the gas? Use the ideal gas law.

Accepted Answer

$$V_2$$ = $$V_1$$ 	imes \frac{$$P_1$$}{$$P_2$$} 	imes \frac{$$T_2$$}{$$T_1$$} = 10.0\,	ext{L} 	imes \frac{2.00}{1.00} 	imes \frac{400}{300} = 26.7\,	ext{L}$$

Question 2

Which of the following intermolecular forces is primarily responsible for the unusually high boiling point of water ($$H_2O$$)?

Accepted Answer

Hydrogen bonding

Question 3

A crystalline solid is found to have a cubic unit cell with an edge length of $$4.00\,	ext{\AA}$$ and a density of $$2.00\,	ext{g/cm}^3. If $$the molar mass of the compound is $$100.0\,	ext{g/mol}$$, how many formula units are present per unit cell?

Accepted Answer

4

Question 4

Which of the following statements best describes the effect of a catalyst on a chemical reaction?

Accepted Answer

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

Question 5

For the reaction $$2NO_2(g) ightarrow 2NO(g) + O_2$(g)$$, the rate law is found to be $$	ext{rate} = k[NO_2$]^2. If $$the concentration of $$NO_2 is $$doubled, how does the rate change?

Accepted Answer

The rate increases by a factor of 4.

Question 6

A reaction has an equilibrium constant $$K_c = 1.0 	imes 10$$^{-5}$$ at 25°C. Which statement is true about the reaction at equilibrium?

Accepted Answer

Reactants are favored over products.

Question 7

Which of the following solutions has the highest pH?

Accepted Answer

0.10 M $$NaOH$$

Question 8

A buffer solution is prepared by mixing equal moles of acetic acid ($$CH_3COOH) $$and sodium acetate ($$CH_3COONa). $$What happens to the pH when a small amount of $$HCl is $$added?

Accepted Answer

The pH decreases slightly.

Question 9

Which of the following best describes the enthalpy change ($$\Delta H) $$for an endothermic reaction?

Accepted Answer

$$\Delta H \u003e 0$$

Question 10

A sample of $$Ca(OH)_2 is $$dissolved in water and the temperature of the solution increases. What can be concluded about the dissolution process?

Accepted Answer

The dissolution is exothermic ($$\Delta H \u003c 0).$$

Question 11

Which of the following statements about the rate-determining step in a reaction mechanism is correct?

Accepted Answer

It is the slowest step in the mechanism and limits the overall reaction rate.

Question 12

Which of the following changes will increase the solubility of a gas in water?

Accepted Answer

Decreasing the temperature and increasing the pressure.

Question 13

A weak acid, $$HA$$, has a $$K_a = 1.0 	imes 10$$^{-5}$$. What is the pH of a 0.10 M solution of HA$? (Assume x$$ \ll 0.10$$)

Accepted Answer

$$pH = 3.0$$

Question 14

Which of the following best explains why $$NH_3 ($$ammonia) is highly soluble in water?

Accepted Answer

It forms hydrogen bonds with water molecules.

Question 15

Which of the following is true for a reaction at equilibrium?

Accepted Answer

The rates of the forward and reverse reactions are equal.

Question 16

A reaction is spontaneous at room temperature but becomes nonspontaneous at high temperature. Which of the following is true about the signs of $$\Delta H$$ and $$\Delta S$$?

Accepted Answer

$$\Delta H \u003c 0$$ and $$\Delta S \u003c 0$$

Question 17

Which of the following is the correct expression for the equilibrium constant $$K_c$$ for the reaction $$N_2(g) + 3H_2(g$$) \rightleftharpoons 2NH_3(g)$$?

Accepted Answer

$$K_c = \frac{[NH_3$]^2}{[N_2$][H_2$]^3}$$

Question 18

Which of the following best describes the structure of a metallic solid?

Accepted Answer

A lattice of positive ions surrounded by a sea of delocalized electrons.

Question 19

A reaction has an activation energy of $$50\,	ext{kJ/mol}$$ without a catalyst and $$20\,	ext{kJ/mol}$$ with a catalyst. At the same temperature, how does the rate constant $$k$$ change?

Accepted Answer

The rate constant increases because the activation energy decreases.

Question 20

Which of the following is a correct statement about the relationship between Gibbs free energy ($$\Delta G$$), enthalpy ($$\Delta H$$), and entropy ($$\Delta S$$)?

Accepted Answer

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

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