Q: A solution is prepared by dissolving 0.5 mol of NaCl in 1.0 kg of water. Calculate the freezing point depression ($$\Delta T_f) $$given $$K_f = 1.86\ \mathrm{^ ext{o}C\ kg\ $$mol^{-1}$$}. $$Assume complete dissociation of NaCl.

$$\Delta T_f = 1.86\ \mathrm{^ ext{o}C} \times 1.0 \times 2 = 1.86\ \mathrm{^ ext{o}C}$$

Q: A solution contains 0.2 mol of KBr dissolved in 0.5 kg of water. What is the boiling point elevation ($$\Delta T_b) if$$ $$K_b = 0.512\ \mathrm{^ ext{o}C\ kg\ $$mol^{-1}$$}$$? Assume complete dissociation.

$$\Delta T_b = 0.512 \times 0.4 = 0.2048\ \mathrm{^ ext{o}C}$$

Question 1

Which of the following best explains why adding a nonvolatile solute to water lowers its vapor pressure?

Accepted Answer

The solute particles occupy surface sites, reducing the number of water molecules able to escape into the vapor phase.

Question 2

A solution is prepared by dissolving 0.5 mol of NaCl in 1.0 kg of water. Calculate the freezing point depression ($$\Delta T_f) $$given $$K_f = 1.86\ \mathrm{^	ext{o}C\ kg\ $$mol^{-1}$$}. $$Assume complete dissociation of NaCl.

Accepted Answer

$$\Delta T_f = 1.86\ \mathrm{^	ext{o}C} 	imes 1.0 	imes 2 = 1.86\ \mathrm{^	ext{o}C}$$

Question 3

Which intermolecular force is primarily responsible for the high solubility of NaCl in water?

Accepted Answer

Ion-dipole interactions

Question 4

A student mixes 0.1 mol of glucose (a non-electrolyte) in 1.0 L of water. What is the molarity of the solution?

Accepted Answer

$$0.1\ \mathrm{M}$$

Question 5

Which of the following would most likely increase the rate of a chemical reaction?

Accepted Answer

Adding a catalyst

Question 6

Given the rate law $$	ext{Rate} = k[A]^2[B]$$, what is the order of reaction with respect to $$A$$ and $$B$$?

Accepted Answer

Second order in $$A$$, first order in $$B$$; overall third order

Question 7

A graph of concentration vs. time for a reaction shows a straight line with a negative slope. What is the order of the reaction?

Accepted Answer

Zero order

Question 8

Which of the following is true about catalysts in a chemical reaction?

Accepted Answer

Catalysts provide an alternative pathway with lower activation energy.

Question 9

A reaction progress diagram shows a peak between reactants and products. What does this peak represent?

Accepted Answer

The activation energy barrier

Question 10

If the rate constant $$k$$ for a first-order reaction is $$0.693\ \mathrm{min}^{-1}$$, what is the half-life ($$t_{1/2}) of $$the reaction?

Accepted Answer

$$t_{1/2} = \dfrac{0.693}{0.693} = 1\ \mathrm{min}$$

Question 11

Which of the following best describes the role of intermediates in a multi-step reaction mechanism?

Accepted Answer

Intermediates are formed and consumed during the reaction but do not appear in the overall equation.

Question 12

A solution contains 0.2 mol of KBr dissolved in 0.5 kg of water. What is the boiling point elevation ($$\Delta T_b) if$$ $$K_b = 0.512\ \mathrm{^	ext{o}C\ kg\ $$mol^{-1}$$}$$? Assume complete dissociation.

Accepted Answer

$$\Delta T_b = 0.512 	imes 0.4 = 0.2048\ \mathrm{^	ext{o}C}$$

Question 13

Which of the following is NOT a factor that affects the rate of a chemical reaction?

Accepted Answer

Color of the reactants

Question 14

A reaction has the following elementary steps:
Step 1: $$A + B \rightarrow C ($$slow)
Step 2: $$C \rightarrow D ($$fast)
What is the rate-determining step?

Accepted Answer

Step 1: $$A + B \rightarrow C$$

Question 15

Which of the following best describes a solvent in a solution?

Accepted Answer

The substance present in the largest amount

Question 16

A graph of $$\ln[A] vs. $$time for a reaction is linear with a negative slope. What is the order of the reaction?

Accepted Answer

First order

Question 17

Which of the following statements about molarity is correct?

Accepted Answer

Molarity is defined as moles of solute per liter of solution.

Question 18

Which of the following is a correct interpretation of the rate constant $$k in a $$second-order reaction?

Accepted Answer

$$k$$ has units of $$\mathrm{L\ $$mol^{-1}$$\ s$$^{-1}$$}$$

Question 19

Which of the following would be the best method to determine the activation energy of a reaction experimentally?

Accepted Answer

Measure the rate constant at different temperatures and use the Arrhenius equation.

Question 20

In a reaction mechanism, which species are present in the elementary steps but not in the overall reaction?

Accepted Answer

Intermediates

General Chemistry Study Notes: Solutions and Kinetics

Guida di studio - Domande di pratica

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