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AP Chemistry Unit 5: Kinetics

12 questions

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Unit 5: Kinetics

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Question 1

A reaction has the energy profile shown below (described): the reactants are at a higher energy than the products, and there is a single energy maximum (transition state) between them. The activation energy for the forward reaction is $80 kJ/mol$ and for the reverse reaction is $120 kJ/mol$ . What is $Δ H$ for the forward reaction?

- 40 kJ/mol

+ 40 kJ/mol

+ 200 kJ/mol

- 120 kJ/mol

Question 2

For a first-order reaction with rate constant $k = 0.0231 mi n^{- 1}$ , what is the half-life?

43.3 min

30.0 min

0.0231 min

1.00 min

Question 3

An Arrhenius plot of $ln k$ vs $1/ T$ gives a straight line with slope $- 8000 K$ . What is the activation energy $E_{a}$ ? ( $R = 8.314 J/ (mol \cdot K)$ )

9.63 kJ/mol

66.5 kJ/mol

8000 kJ/mol

960 kJ/mol

Question 4

Which statement correctly describes how a catalyst increases reaction rate?

A.A catalyst increases the temperature of the reaction, giving molecules more kinetic energy.B.A catalyst is consumed in the reaction, producing more product.C.A catalyst provides an alternative pathway with a lower activation energy, increasing the fraction of successful collisions.D.A catalyst shifts the equilibrium toward products by raising

Δ G

Question 5

A proposed mechanism for a reaction is:

Step 1 (slow): $N O_{2} + N O_{2} \to N O_{3} + NO$

Step 2 (fast): $N O_{3} + CO \to N O_{2} + C O_{2}$

What is the overall reaction and the predicted rate law?

A.Overall:

N O_{2} + CO \to NO + C O_{2}

; rate

= k [N O_{2}] [CO]

B.Overall:

N O_{2} + CO \to NO + C O_{2}

; rate

= k [N O_{2}]^{2}

C.Overall:

2 N O_{2} + CO \to N O_{3} + NO + C O_{2}

; rate

= k [N O_{2}]^{2} [CO]

D.Overall:

N O_{2} + CO \to NO + C O_{2}

; rate

= k [N O_{3}] [CO]

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Question 6

Which of the following best describes the orientation and energy requirements for an effective collision in collision theory?

A.Any collision produces a reaction; increasing collision frequency always increases rate.B.Only collisions with energy

\geq E_{a}

AND correct geometric orientation lead to reaction.C.Orientation does not matter; only the kinetic energy of the collision is important.D.Energy is irrelevant; rate depends only on the frequency of correctly oriented collisions.

Question 7

What distinguishes a homogeneous catalyst from a heterogeneous catalyst?

A.A homogeneous catalyst is consumed in the reaction, while a heterogeneous catalyst is not.B.A homogeneous catalyst is in the same phase as the reactants; a heterogeneous catalyst is in a different phase.C.A homogeneous catalyst lowers activation energy; a heterogeneous catalyst does not.D.Homogeneous catalysts are always biological (enzymes); heterogeneous are always metals.

Question 8

The rate of decomposition of $N_{2} O_{5}$ is measured at two temperatures:

Temperature	Rate constant $k$
$25° C$	$3.0 \times 1 0^{- 5} s^{- 1}$
$45° C$	$1.2 \times 1 0^{- 4} s^{- 1}$

Which statement about this data is correct?

A.The reaction rate doubles for every

10° C

increase because that is a chemistry rule.B.The rate constant increases by a factor of 4 over a 20°C range, consistent with Arrhenius behavior.C.The rate constant doubles when temperature is doubled, so the reaction is second order in temperature.D.The rate constant is independent of temperature for a first-order reaction.

Question 9

The concentration of a reactant A in a first-order reaction decreases from $0.800 M$ to $0.100 M$ over $90 min$ . What is the half-life of the reaction?

11.25 min

30 min

45 min

90 min

Question 10

For the reaction $A + B \to C$ , tripling $[A]$ while keeping $[B]$ constant triples the reaction rate. Tripling $[B]$ while keeping $[A]$ constant has no effect on the rate. What is the rate law?

rate = k [A] [B]

rate = k [A]

rate = k [A]^{2}

rate = k [B]

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Question 11

For the reaction $2 N O_{2} (g) \to 2 NO (g) + O_{2} (g)$ , experimental data shows that doubling $[N O_{2}]$ increases the initial rate by a factor of 4. What is the rate law and overall reaction order?

rate = k [N O_{2}]

; first order overallB.

rate = k [N O_{2}]^{2}

; second order overallC.

rate = k [N O_{2}]^{2} [NO] [O_{2}]

; fourth order overallD.

rate = k [N O_{2}]^{1/2}

; half order overall

Question 12

For the second-order integrated rate law $\frac{1}{[ A ] _{t}} = k t + \frac{1}{[ A ] _{0}}$ , if $[A]_{0} = 0.500 M$ and $k = 0.0400 M^{- 1} \cdot s^{- 1}$ , what is $[A]$ after $100 s$ ?

0.167 M

0.250 M

0.100 M

0.333 M

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