Q: Given the reaction mechanism: Step 1 (fast): $$A + B \rightleftharpoons 2A$$ Step 2 (slow): $$A + 2B \rightarrow 2AB ($$overall reaction) What is the rate law for the overall reaction?

$$\text{Rate} = k[A]^{1/2}[B]$$

Q: Hydrogen iodide decomposes at 800 K via a second-order process to produce hydrogen and iodine. If it takes 142 seconds for the initial concentration of HI to decrease from $$6.75 \times 10$$^{-2}$$ \text{ M} to$$ $$3.51 \times 10$$^{-2}$$ \text{ M}$$, what is the rate constant for the reaction at this temperature?

$$9.69 \times 10$$^{-3}$$ \text{ M}^{-1}\text{s}^{-1}$$

Question 1

A compound with a molar mass of 598 g/mol is dissolved in enough water to make 175 mL of solution at 25°C. If 35.8 mg of the compound is used, what is the osmotic pressure of the solution? (Use $$R = 0.08206 	ext{ L atm/mol K}$$ and convert your answer to torr.)

Accepted Answer

6.36 torr

Question 2

A solution contains 5.0 grams of KCl and 550.0 grams of water. What is the freezing point of the solution? ($$K_f$$ for water is $$1.86 	ext{°C kg/mol}$$, molar mass of KCl is $$74.5513 	ext{ g/mol}$$, assume ideal behavior.)

Accepted Answer

$$-0.45 	ext{°C}$$

Question 3

Given the reaction $$2NO(g) + Cl_2$(g) \rightarrow 2NOCl(g)$$, which expression correctly represents the rate of appearance of NOCl?

Accepted Answer

$$\frac{1}{2} \frac{\Delta [NOCl]}{\Delta t}$$

Question 4

Experimental data for the reaction $$2SO_2(g) + O_2$(g) \rightarrow 2SO_3(g) is $$given below:

$$[SO_2$] (M$$): 0.44, 0.44, 0.21
$$[O_2$] (M$$): 0.21, 0.44, 0.21
Initial Rate ($$M/s$$): 6.65, 13.3, 3.33

What is the order of the reaction with respect to $$SO_2$$?

Accepted Answer

First order

Question 5

Which plot should be used to determine if a reaction is first order with respect to reactant concentration?

Accepted Answer

$$\ln [A] vs. $$time

Question 6

The rate constant for the first-order decomposition of $$N_2O is$$ $$3.40 	ext{ s}^{-1}. $$What is the half-life of the reaction?

Accepted Answer

$$0.204 	ext{ s}$$

Question 7

For a second-order reaction, the integrated rate law is:

Accepted Answer

$$\frac{1}{[A]_t} = kt + \frac{1}{[A]_0}$$

Question 8

The second-order decomposition of HI has a rate constant of $$1.80 	imes 10$$^{-3}$$ 	ext{ M}^{-1}	ext{s}^{-1}. $$How much HI remains after 27.3 s if the initial concentration is 4.78 M?

Accepted Answer

3.87 M

Question 9

A first-order rearrangement of $$CH_3NC is $$measured to have a rate constant of $$3.61 	imes 10$$^{-15}$$ 	ext{ s}^{-1} at 298 K $$and $$8.66 	imes 10$$^{-7}$$ 	ext{ s}^{-1} at 425 K. $$What is the activation energy for this reaction?

Accepted Answer

160 kJ/mol

Question 10

Given the reaction mechanism:
Step 1 (fast): $$A + B \rightleftharpoons 2A$$
Step 2 (slow): $$A + 2B \rightarrow 2AB ($$overall reaction)
What is the rate law for the overall reaction?

Accepted Answer

$$	ext{Rate} = k[A]^{1/2}[B]$$

Question 11

For the reaction $$X + 3Y ightarrow 2Z$$, the rate law is $$	ext{Rate} = k[X][Y]^2. $$What is the overall order of the reaction?

Accepted Answer

Third order

Question 12

Hydrogen iodide decomposes at 800 K via a second-order process to produce hydrogen and iodine. If it takes 142 seconds for the initial concentration of HI to decrease from $$6.75 	imes 10$$^{-2}$$ 	ext{ M} to$$ $$3.51 	imes 10$$^{-2}$$ 	ext{ M}$$, what is the rate constant for the reaction at this temperature?

Accepted Answer

$$9.69 	imes 10$$^{-3}$$ 	ext{ M}^{-1}	ext{s}^{-1}$$

Question 13

Which of the following changes will shift the equilibrium of an exothermic reaction to the left?

Accepted Answer

Increasing temperature

Question 14

For the equilibrium $$N_2O_4(g) \rightleftharpoons 2NO_2(g)$$, which of the following will increase the amount of $$NO_2 at $$equilibrium?

Accepted Answer

Increasing the volume of the container

Question 15

Which statement about the equilibrium constant $$K is $$TRUE?

Accepted Answer

It is independent of initial concentrations and depends only on temperature.

Question 16

A solution is prepared by dissolving 0.10 mol of NaCl in 1.0 kg of water. What is the boiling point elevation? ($$K_b$$ for water is $$0.512 	ext{°C kg/mol}$$, assume complete dissociation.)

Accepted Answer

$$0.102 	ext{°C}$$

Question 17

Which of the following is NOT a valid assumption for the 'x is small' approximation in equilibrium calculations?

Accepted Answer

The equilibrium constant $$K is $$very large.

Question 18

Which of the following statements about reaction mechanisms is FALSE?

Accepted Answer

The rate law for the overall reaction can always be determined from the balanced equation.

Question 19

A reaction has a rate constant $$k at 298 K. If $$the activation energy is 160 kJ/mol, what will happen to the rate constant if the temperature is increased to 425 K?

Accepted Answer

The rate constant will increase significantly.

General Chemistry Study Notes: Colligative Properties, Chemical Kinetics, and Reaction Mechanisms

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