Q: If the rate-determining step in a reaction mechanism is $$\mathrm{Cl (g) + $$CHCl_3$$ (g) \rightarrow HCl (g) + $$CCl_3$$ (g)}$$, what is the predicted rate law?

$$\text{Rate} = k[Cl][$$CHCl_3$$]$$

Question 1

Which of the following best describes the activation energy ($$E_a) in a $$reaction energy diagram?

Accepted Answer

The minimum energy required for reactants to form products.

Question 2

Given the Arrhenius equation $$k = Ae$$^{-E_a/RT}$$, what does the pre-exponential factor A$ represent?

Accepted Answer

The frequency of collisions with the correct orientation.

Question 3

A plot of $$\ln k$$ versus $$1/T$$ for a reaction yields a straight line with a slope of $$-7012 K. $$What is the activation energy ($$E_a) in kJ/$$mol? (Use $$R = 8.314 J/$$mol·K)

Accepted Answer

$$E_a = 58.3 kJ/$$mol

Question 4

For the reaction mechanism:

$$\mathrm{Cl_2$ (g) \rightleftharpoons 2Cl (g)} ($$fast)
$$\mathrm{Cl (g) + $$CHCl_3$$ (g) \rightarrow HCl (g) + $$CCl_3$$ (g)} ($$slow)
$$\mathrm{Cl (g) + $$CCl_3$$ (g) \rightarrow $$CCl_4$$ (g)} ($$fast)

Which species are intermediates?

Accepted Answer

$$\mathrm{Cl}$$ and $$\mathrm{$$CCl_3$$}$$

Question 5

Given the following data for a reaction:
$$k_1 = 0.0117$$\ \mathrm{$$s^{-1}$$}$$ at T_1$ = 400.0\ \mathrm{K}$$
$$k_2 = 0.689$$\ \mathrm{$$s^{-1}$$}$$ at T_2$ = 450.0\ \mathrm{K}$$
Calculate the activation energy $$E_a in J/$$mol using the two-point Arrhenius equation.

Accepted Answer

$$E_a = 121,975 J/$$mol

Question 6

Which of the following is the correct linearized form of the Arrhenius equation?

Accepted Answer

$$\ln k = -\frac{E_a}{R} \left( \frac{1}{T} \right) + \ln A$$

Question 7

If the rate-determining step in a reaction mechanism is $$\mathrm{Cl (g) + $$CHCl_3$$ (g) \rightarrow HCl (g) + $$CCl_3$$ (g)}$$, what is the predicted rate law?

Accepted Answer

$$	ext{Rate} = k[Cl][$$CHCl_3$$]$$

Question 8

A reaction has a rate constant of $$0.0117\ \mathrm{s$$^{-1}$$} at$$ $$400.0\ \mathrm{K}$$ and $$0.689\ \mathrm{s$$^{-1}$$} at$$ $$450.0\ \mathrm{K}. $$What is the value of the rate constant at $$425\ \mathrm{K}$$?

Accepted Answer

$$k = 0.090\ \mathrm{s$$^{-1}$$}$$

Question 9

Which of the following statements about reaction intermediates is correct?

Accepted Answer

Intermediates are formed and consumed during the reaction mechanism.

Question 10

Which of the following best describes the overall reaction for the given mechanism?

$$\mathrm{Cl_2$ (g) + $$CHCl_3$$ (g) \rightarrow HCl (g) + $$CCl_4$$ (g)}$$

Accepted Answer

It is the sum of all elementary steps, canceling intermediates.

Question 11

Which of the following is NOT a correct unit for the gas constant $$R$$?

Accepted Answer

$$760\ \mathrm{L \cdot atm / mol \cdot K}$$

Question 12

Which of the following best explains why increasing temperature generally increases the rate constant $$k$$ for a reaction?

Accepted Answer

It increases the number of molecules with sufficient energy to overcome the activation barrier.

Question 13

A student claims that the rate law for a reaction can always be written directly from the overall balanced equation. Is this correct?

Accepted Answer

No, because the rate law depends on the slowest step in the mechanism.

Question 14

Which of the following is the correct two-point form of the Arrhenius equation?

Accepted Answer

$$\ln \frac{k_2$}{k_1$} = \frac{E_a}{R} \left( \frac{1}{T_1$} - \frac{1}{T_2$} \right)$$

Question 15

Which of the following is a correct conversion for pressure?

Accepted Answer

$$1\ \mathrm{atm} = 760\ \mathrm{torr}$$

General Chemistry Exam Review: Kinetics, Reaction Mechanisms, and Arrhenius Equation

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