Q: A solution is prepared by dissolving 0.5 mol of NaCl in 1 kg of water. Given $$K_f = 1.86\ \mathrm{^\\circ C\ kg\ $$mol^{-1}$$}$$ for water, what is the expected freezing point depression? (Assume complete dissociation of NaCl.)

$$\\Delta T_f = 1.86^\\circ C$$

Q: Which of the following is the correct integrated rate law for a first-order reaction?

$$\\ln [A]_t = -kt + \\ln [A]_0$$

Question 1

Which of the following best describes why the freezing point of a solution is lower than that of the pure solvent?

Accepted Answer

The solute particles disrupt the formation of the solid structure, requiring a lower temperature to freeze.

Question 2

A solution is prepared by dissolving 0.5 mol of NaCl in 1 kg of water. Given $$K_f = 1.86\ \mathrm{^\circ C\ kg\ $$mol^{-1}$$}$$ for water, what is the expected freezing point depression? (Assume complete dissociation of NaCl.)

Accepted Answer

$$\Delta T_f = 1.86^\circ C$$

Question 3

Which of the following equations correctly represents the osmotic pressure of a solution containing a strong electrolyte?

Accepted Answer

$$\Pi = iMRT$$

Question 4

For the reaction $$2NO + Cl_2$ \rightarrow 2NOCl$$, the rate law is $$\text{rate} = k[NO]^2[Cl_2$]. $$What is the overall order of the reaction?

Accepted Answer

Third order

Question 5

A reaction is first-order in X. If the rate constant $$k = 0.693\ \mathrm{s$$^{-1}$$}$$, what is the half-life of the reaction?

Accepted Answer

$$t_{1/2} = 1.00\ \mathrm{s}$$

Question 6

Which of the following changes will increase the rate of a chemical reaction according to collision theory?

Accepted Answer

Increasing the concentration of reactants

Question 7

Given the following mechanism for a reaction:
1. $$NO + O_2$ \rightarrow NO_2$ + O ($$slow)
2. $$O + NO \rightarrow NO_2$ (fast)
What is the predicted rate law for the overall reaction?

Accepted Answer

$$\text{Rate} = k[NO][O_2$]$$

Question 8

Which of the following statements about colligative properties is correct?

Accepted Answer

They depend on the number of dissolved particles.

Question 9

A solution is made by dissolving 0.1 mol of glucose (a non-electrolyte) in 1 kg of water. What is the van’t Hoff factor ($$i) $$for this solution?

Accepted Answer

$$i = 1$$

Question 10

The rate constant $$k$$ for a reaction increases by a factor of 4 when the temperature is increased from 300 K to 320 K. Which of the following best explains this observation?

Accepted Answer

The activation energy is high, so temperature has a large effect.

Question 11

Which of the following best describes osmosis?

Accepted Answer

The flow of solvent from a solution of lower solute concentration to one of higher solute concentration.

Question 12

Which of the following is the correct integrated rate law for a first-order reaction?

Accepted Answer

$$\ln [A]_t = -kt + \ln [A]_0$$

Question 13

A reaction has a rate law $$\text{rate} = k[A][B]^2. $$What are the units of the rate constant $$k$$?

Accepted Answer

$$M^{-2}$$ $$s^{-1}$$

Question 14

Which of the following graphs would be linear for a second-order reaction?

Accepted Answer

$$\frac{1}{[A]} vs. $$time

Question 15

Which of the following best explains why salt is spread on icy roads in winter?

Accepted Answer

Salt decreases the freezing point of water.

Question 16

The activation energy $$E_a$$ for a reaction can be determined from the slope of a plot of $$\ln k vs$$. $$\frac{1}{T}. If $$the slope is $$-19000\ \mathrm{K}$$, what is $$E_a in$$ $$\mathrm{J/mol}$$? (Use $$R = 8.314\ \mathrm{J/(mol\ K)})$$

Accepted Answer

$$E_a = 158,000\ \mathrm{J/mol}$$

Question 17

Which of the following is NOT a colligative property?

Accepted Answer

Viscosity

Question 18

A reaction is second-order in A. If the initial concentration of A is doubled, how does the initial rate change?

Accepted Answer

It quadruples.

Question 19

Which of the following best describes the energetics of solution formation for an endothermic process?

Accepted Answer

The energy required to separate solute and solvent particles is greater than the energy released when they mix.

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