Q: For the reaction $$A \rightarrow B$$, which formula correctly expresses the rate of disappearance of $$A$$?

$$\text{vitesse} = -\frac{\Delta [A]}{\Delta t}$$

Q: Given the reaction $$2A + 3B \rightarrow 4C + D$$, which expression correctly relates the rate of change of each species?

$$\text{vitesse} = -\frac{1}{2}\frac{\Delta [A]}{\Delta t} = -\frac{1}{3}\frac{\Delta [B]}{\Delta t} = \frac{1}{4}\frac{\Delta [C]}{\Delta t} = \frac{\Delta [D]}{\Delta t}$$

Q: A first-order reaction has a half-life of 84.1 min. What is the value of the rate constant $$k$$?

$$k = \frac{\ln 2}{84.1\ \text{min}} = 8.23 \times 10$$^{-3}$$\ \text{min}^{-1}$$

Question 1

Which of the following best describes the rate of a chemical reaction?

Accepted Answer

The rate of reaction is the variation of the concentration of a reactant or product over time.

Question 2

For the reaction $$A \rightarrow B$$, which formula correctly expresses the rate of disappearance of $$A$$?

Accepted Answer

$$	ext{vitesse} = -\frac{\Delta [A]}{\Delta t}$$

Question 3

Given the reaction $$2A + 3B \rightarrow 4C + D$$, which expression correctly relates the rate of change of each species?

Accepted Answer

$$	ext{vitesse} = -\frac{1}{2}\frac{\Delta [A]}{\Delta t} = -\frac{1}{3}\frac{\Delta [B]}{\Delta t} = \frac{1}{4}\frac{\Delta [C]}{\Delta t} = \frac{\Delta [D]}{\Delta t}$$

Question 4

Which statement about the rate law is correct?

Accepted Answer

The rate law expresses the rate of reaction as a function of the concentrations of reactants, each raised to a power determined experimentally.

Question 5

For the reaction $$F_2(g) + 2$$ClO_2(g) \rightarrow 2FClO_2(g)$$, the initial rate doubles when $$[$$F_2$$]$$ is doubled, but quadruples when $$[$$ClO_2$$]$$ is doubled. What is the correct rate law?

Accepted Answer

$$v = k[F_2$][$$ClO_2$$]^2$$

Question 6

If a reaction is first order in $$A$$, which integrated rate law describes the change in $$[A]$$ over time?

Accepted Answer

$$\ln \left( \frac{[A]_0}{[A]} \right) = kt$$

Question 7

A first-order reaction has a half-life of 84.1 min. What is the value of the rate constant $$k$$?

Accepted Answer

$$k = \frac{\ln 2}{84.1\ 	ext{min}} = 8.23 	imes 10$$^{-3}$$\ 	ext{min}^{-1}$$

Question 8

Which factor does NOT affect the rate constant $$k of a $$reaction?

Accepted Answer

The concentration of reactants

Question 9

According to the Arrhenius equation, how does the rate constant $$k$$ change with increasing temperature?

Accepted Answer

$$k$$ increases exponentially with temperature

Question 10

Which equation correctly represents the Arrhenius equation?

Accepted Answer

$$k = Ae$$^{-E_a/(RT)}$$

Question 11

For a reaction $$A \rightarrow B$$ that is first order in $$A$$, what is the expression for the half-life $$t_{1/2}$$?

Accepted Answer

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

Question 12

Which statement about reaction mechanisms is correct?

Accepted Answer

The rate law for a reaction is determined by the slowest (rate-determining) step in the mechanism.

Question 13

In the decomposition of hydrogen peroxide, $$2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2$(g)$$, which species acts as a catalyst in the proposed mechanism?

Accepted Answer

$$I^-$$

Question 14

If the rate law for a reaction is $$v = k[A]^2[B]$$, what is the overall order of the reaction?

Accepted Answer

3

Question 15

Which of the following is true for a zero-order reaction?

Accepted Answer

The rate of reaction is independent of the concentration of reactant.

Question 16

A reaction has a rate law $$v = k[A][B]. If$$ $$[A] is $$doubled and $$[B] is $$tripled, by what factor does the rate increase?

Accepted Answer

6

Question 17

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

Accepted Answer

It increases the number of molecules with energy greater than the activation energy.

Question 18

For a first-order reaction, which plot yields a straight line?

Accepted Answer

$$\ln [A]$$ versus $$t$$

La cinétique chimique (Chemical Kinetics): Study Notes

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