Question 1

Which of the following statements best explains why increasing the temperature generally increases the rate of a chemical reaction?

Accepted Answer

Because higher temperature increases the fraction of molecules with energy greater than the activation energy ($$E_a).$$

Question 2

The Arrhenius equation is given by $$k = Ae$$^{-E_a/(RT)}$$. What does the term A$ represent in this equation?

Accepted Answer

The frequency factor, which includes the steric factor and collision frequency.

Question 3

A reaction has a rate law $$R = k[	ext{halide}][	ext{OH}^-]. If $$the concentration of halide is doubled and the concentration of OH$$^- is $$tripled, by what factor does the reaction rate increase?

Accepted Answer

The rate increases by a factor of 6.

Question 4

In a reaction coordinate diagram, what does the highest point along the reaction pathway represent?

Accepted Answer

The transition state, which corresponds to the maximum energy point.

Question 5

Which of the following changes will NOT increase the rate of a reaction?

Accepted Answer

Decreasing the concentration of one of the reactants.

Question 6

A certain reaction has a large activation energy ($$E_a). $$Which of the following is most likely true about this reaction at room temperature?

Accepted Answer

The reaction will proceed slowly because few molecules have enough energy to overcome $$E_a.$$

Question 7

The rate-limiting step in a multi-step reaction mechanism is best described as:

Accepted Answer

The slowest step, which has the highest activation energy.

Question 8

If a reaction is first order in A and second order in B, what is the correct rate law for the reaction?

Accepted Answer

$$R = k[A][B]^2$$

Question 9

Which of the following best describes the effect of a catalyst on a chemical reaction?

Accepted Answer

It lowers the activation energy ($$E_a) $$and increases the reaction rate.

Question 10

A reaction has a rate constant $$k$$ that increases from $$1.0 	imes 10$$^{-3}$$\ 	ext{M}^{-1}	ext{s}^{-1} to$$ $$4.0 	imes 10$$^{-3}$$\ 	ext{M}^{-1}	ext{s}^{-1}$$ when the temperature is increased from $$300\ 	ext{K} to$$ $$310\ 	ext{K}. $$Which of the following best explains this observation?

Accepted Answer

The fraction of molecules with energy greater than $$E_a$$ increases with temperature.

Question 11

In a real-world scenario, the decomposition of hydrogen peroxide ($$2H_2O_2 \rightarrow 2H_2O + O_2$) is slow at room temperature but speeds up dramatically in the presence of manganese dioxide ($$MnO_2$$). What role does $$MnO_2$$ play in this reaction?

Accepted Answer

It acts as a catalyst by providing an alternative pathway with lower activation energy.

Question 12

Which of the following factors is represented by the 'steric factor' in the Arrhenius equation?

Accepted Answer

The probability that molecules will collide with the correct orientation to react.

Question 13

A student measures the rate of a reaction and finds that doubling the concentration of one reactant doubles the rate, but doubling the other reactant quadruples the rate. What is the most likely rate law for this reaction?

Accepted Answer

$$R = k[A][B]^2$$

Question 14

Which of the following best describes the relationship between the rate constant $$k$$ and temperature $$T$$ according to the Arrhenius equation?

Accepted Answer

$$k$$ increases exponentially with increasing $$T.$$

Question 15

In a reaction coordinate diagram, what does the difference in energy between the reactants and the transition state represent?

Accepted Answer

The activation energy ($$E_a) of $$the reaction.

Question 16

A certain reaction is found to be zero order with respect to reactant A. Which of the following statements is true?

Accepted Answer

The rate of the reaction does not depend on the concentration of A.

Question 17

In a medical context, the breakdown of a drug in the liver often follows first-order kinetics. If the half-life of the drug is 4 hours, how much of the drug remains after 12 hours?

Accepted Answer

One-eighth of the original amount.

Question 18

Which of the following is a correct interpretation of the slope in a plot of concentration versus time for a zero-order reaction?

Accepted Answer

The slope is constant and equal to $$-k.$$

Question 19

A reaction has the following rate law: $$R = k[A]^2. If $$the initial concentration of A is $$0.10\ 	ext{M}$$ and the rate constant $$k is$$ $$2.0\ 	ext{M}^{-1}	ext{s}^{-1}$$, what is the initial rate of the reaction?

Accepted Answer

$$0.02\ 	ext{M}\cdot	ext{s}^{-1}$$

Chemical Kinetics: Activation Energy, Reaction Rates, and Reaction Coordinate Diagrams

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