Chemistry: Molecular Nature of Matter and Change, 6th Edition (Silberberg)

Chapter 16: Kinetics: Rates and Mechanisms of Chemical Reactions

Self-Assessment Quiz 1

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1
For the overall hypothetical reaction A + 5B → 4C, the rate of appearance of C given by Δ[C]/Δt is the same as
A)Δ[A]/Δt
B)-(5/4)(Δ[B]/Δt)
C)-(4/5)(Δ[B]/Δt)
D)-(1/4)(Δ[A]/Δt)
E)none of the above.
2
When heated, the compound RX3 decomposes to a mixture of products. The following data were collected for the decomposition at 100º C. What is the average rate of reaction, -Δ [RX3]/Δt, over the entire experiment?
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A)0.0028 mol/L.s
B)0.045 mol/L.s
C)0.0014 mol/L.s
D)-0.0027 mol/L.s
E)0.0057 mol/L.s
3
The initial rate of the reaction PCl5 → PCl3 + Cl2 is increased a factor of four when the concentration of PCl5is doubled. Therefore, the rate
A)depends on the concentrations of PCl3 and Cl2.
B)is first order with respect to PCl5.
C)is second order with respect to PCl5.
D)is fourth order with respect to PCl5.
E)is first order with respect to PCl3.
4
Bromine atoms react with iso-butane (iso-C4H10) to form hydrogen bromide and the t-butyl radical (t-C4H9): Br + iso-C4H10 → HBr + t-C4H9. The reaction is first order with respect to each of the reactants, and at 298 K, the rate constant is 1.02 x 106 L mol-1 s-1. Calculate the initial rate of the reaction in a 4.0 L reaction vessel containing 0.60 moles of iso-butane and 0.00010 moles of bromine atoms.
A)1.5 mol L-1 s-1
B)3.8 mol L-1 s-1
C)2.5 x 1011 mol L-1 s-1
D)2.5 x 102 mol L-1 s-1
E)6.7 x 102 mol L-1 s-1
5
Consider the thermal decomposition of cyclobutane (C4H8(g)) at 438º C, C4H8(g) → 2C2H4(g). The reaction follows first-order kinetics and the rate constant is k = 2.48 x 10-4 s-1. If the initial concentration of cyclobutane is 0.800 mol/L, what concentration will remain after 10.0 min?
A)0.689 mol/L
B)0.455 mol/L
C)0.333 mol/L
D)0.248 mol/L
E)0.0061 mol/L
6
A certain first-order reaction is 46 % complete in 68 min at 25°C. What is its rate constant?
A)9.1 x 10-3 min-1
B)1.1 x 10-2 min-1
C)31 min-1
D)51 min-1
E)none of the above
7
Consider the reaction A → products. Which, if any, of the following plots is consistent with a second-order reaction?
A)ln[A] plotted against time gives a straight line of positive slope.
B)ln[A] plotted against time gives a straight line of negative slope.
C)1/[A] plotted against time gives a straight line of positive slope.
D)1/[A] plotted against time gives a straight line of negative slope.
E)None of the above plots is consistent with a second-order reaction.
8
Consider the reaction A → products. Which of the following plots is consistent with a zero-order reaction?
A)[A] plotted against time gives a horizontal, straight line.
B)ln[A] plotted against time gives a straight line of negative slope.
C)1/[A] plotted against time gives a straight line of positive slope.
D)[A] plotted against time gives a straight line of negative slope.
E)[A] plotted against time gives a curved line of negative slope, decreasing in magnitude as time increases.
9
What is the value of the rate constant for a first-order reaction for which the half-life is 26.7 min?
A)18.5 min-1
B)38.5 min-1
C)9.25 min-1
D)19.3 min-1
E)0.0260 min-1
10
The rate constant of a first-order reaction is 3.68 x 10-2 s-1 at 150°C, and the activation energy is 71 kJ/mol. What is the value of the rate constant at 170°C?
A)9.2 x 10-2 s-1
B)3.7 x 10-2 s-1
C)2.49 s-1
D)4.0 x 10-2 s-1
E)none of the above
11
In order to obtain the activation energy of a reaction using a graphical method, __________ is plotted against _________, giving a straight line whose slope is equal to __________.
A)k; T; -Ea
B)k; 1/T; -Ea
C)lnk; T; -Ea/R
D)k; 1/T; -Ea/R
E)lnk; 1/T; -Ea/R
12
Select the appropriate rate law for the elementary process shown below.
2A → B + C
A)Rate = k[2A]
B)Rate = k[A]
C)Rate = k[A]2
D)Rate = k[A]1/2
E)Rate = 2k[A]
13
The reaction
3ClO-(aq) → ClO3-(aq)
+ 2Cl-(aq) has been proposed to occur by the following mechanism.
ClO-(aq) + ClO-( aq)→ ClO2-( aq) + Cl-( aq) (slow)
ClO2-(aq) + ClO-(aq) → ClO3-(aq) + Cl-(aq) (fast
Which rate law is consistent with this mechanism?
A)rate = k[ClO-]
B)rate = k[ClO-]3
C)rate = k[ClO2-][ClO-]
D)rate = k[ClO-]2
E)rate = k[Cl-][ClO-]2
14
Consider the reaction:
2NO(g) + 2H2(g) → N2(g) + 2H2O(g)
A suggested mechanism for this reaction follows:
(1) NO(g) + NO(g) → N2O4(g) (slow)
(2) N2O4(g) + H2(g) → N2(g) + H2O2 (g) (fast)
(3) H2O2(g) + H2(g) → 2H2O(g) (fast)
Based on this mechanism, which, if any, of the following actions will not affect the rate of the reaction?
A)adding a catalyst
B)adding more NO(g)
C)adding more H2(g)
D)increasing the temperature
E)All of these will affect the rate of the reaction.
15
A catalyst speeds up a reaction by
A)increasing the number of high-energy molecules.
B)increasing the temperature of the molecules in the reaction.
C)increasing the number of collisions between molecules.
D)increasing the activation energy for the reaction.
E)providing a new reaction pathway for molecules.
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