Q: For a reaction with an activation energy ($$E_a) of 100 kJ/$$mol at 300 K, what is the fraction of molecules with energy greater than or equal to $$E_a$$? (Use $$R = 8.314 J/$$mol·K)

$$f = e$$^{-Ea/RT}$$ = e$$^{-100,000/(8.314 \times 300)}$$ \approx 1.5 \times 10$$^{-18}$$

Question 1

Which of the following best explains why a powdered medicine dissolves and acts faster in the stomach than the same medicine in tablet form?

Accepted Answer

Powdered medicine has a larger surface area, allowing for more immediate interaction with stomach fluids.

Question 2

A reaction is carried out at two different concentrations of reactant A. When [A] is doubled, the rate quadruples. What is the order of the reaction with respect to A?

Accepted Answer

Second order

Question 3

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 4

For the reaction $$2HI(g) \rightarrow H_2$(g) + I_2$(g)$$, which expression correctly relates the rate of disappearance of HI to the rate of appearance of $$I_2$$?

Accepted Answer

$$-\frac{1}{2} \frac{\Delta [HI]}{\Delta t} = \frac{\Delta [I_2$]}{\Delta t}$$

Question 5

A catalyst increases the rate of a chemical reaction by:

Accepted Answer

Lowering the activation energy ($$E_a) of $$the reaction

Question 6

Which of the following statements about the rate constant $$k is $$correct?

Accepted Answer

The units of $$k$$ depend on the overall order of the reaction.

Question 7

The half-life ($$t_{1/2}) $$for a first-order reaction is given by which equation?

Accepted Answer

$$t_{1/2} = \frac{0.693}{k}$$

Question 8

Which of the following best describes the rate-determining step in a multi-step reaction mechanism?

Accepted Answer

It is the slowest elementary step, which limits the overall reaction rate.

Question 9

For a reaction with an activation energy ($$E_a) of 100 kJ/$$mol at 300 K, what is the fraction of molecules with energy greater than or equal to $$E_a$$? (Use $$R = 8.314 J/$$mol·K)

Accepted Answer

$$f = e$$^{-Ea/RT}$$ = e$$^{-100,000/(8.314 	imes 300)}$$ \approx 1.5 	imes 10$$^{-18}$$

Question 10

Which of the following is true about the rate law for an elementary bimolecular reaction?

Accepted Answer

The rate law is second order and depends on the concentration of both reactants.

Question 11

A reaction has the following rate law: $$	ext{Rate} = k[NH_4$^+][NO_2$^-]. If $$the concentration of $$NH_4$$^+$$ is doubled while NO_2$^- is $$kept constant, what happens to the rate?

Accepted Answer

The rate doubles.

Question 12

Which of the following best describes a reaction intermediate?

Accepted Answer

A species that is formed in one step and consumed in a subsequent step of a reaction mechanism.

Question 13

Which of the following is the correct Arrhenius equation relating the rate constant $$k to $$temperature $$T$$?

Accepted Answer

$$k = A e$$^{-E_a/RT}$$

Question 14

Which of the following is a real-life example of heterogeneous catalysis?

Accepted Answer

The use of platinum in catalytic converters to convert CO to CO$$_2 in $$car exhaust.

Question 15

Which of the following statements about enzymes is correct?

Accepted Answer

Enzymes are biological catalysts that increase reaction rates by lowering activation energy.

Question 16

If a reaction is first-order in A and zero-order in B, what is the rate law?

Accepted Answer

$$	ext{Rate} = k[A]$$

Question 17

Which of the following best explains why food spoils more slowly in a refrigerator than at room temperature?

Accepted Answer

Lower temperature decreases the kinetic energy of molecules, reducing the rate of spoilage reactions.

Question 18

Which of the following is true about the units of the rate constant $$k$$ for a second-order reaction?

Accepted Answer

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

Question 19

Which of the following is a requirement for a successful collision between reactant molecules according to the collision model?

Accepted Answer

Reactant molecules must collide with sufficient energy and proper orientation.

Chemical Kinetics: Factors Affecting Reaction Rates and Mechanisms

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