At elevated temperatures, dinitrogen pentoxide decomposes to nitrogen dioxide and oxygen:
2N2O5(g) → 4NO2 (g) + O2 (g)
When the rate of formation of O2 is 2.2 × 10-4 M/s, the rate of decomposition of N2O5 is __________ M/s.
A) 1.1 × 10-4
B) 2.2 × 10-4
C) 2.8 × 10-4
D) 4.4 × 10-4
E) 5.5 × 10-4
Which one of the following is not a valid expression for the rate of the reaction below?
4NH3 + 7O2 → 4NO2 + 6H2O
A)
B)
C)
D)
E) All of the above are valid expressions of the reaction rate.
The rate law of a reaction is rate = k[D][X]. The units of the rate constant are __________.
A) mol L-1s-1
B) L mol-1s-1
C) mol2 L-2s-1
D) mol L-1s-2
E) L2 mol -2s-1
The rate law for this reaction is rate = __________.
A) k[A][B]
B) k[P]
C) k[A]2[B]
D) k[A]2[B]2
E) k[A]2
Under constant conditions, the half-life of a first-order reaction __________.
A) is the time necessary for the reactant concentration to drop to half its original value
B) is constant
C) can be calculated from the reaction rate constant
D) does not depend on the initial reactant concentration
E) All of the above are correct.
The reaction
2NO2 → 2NO + O2
follows second-order kinetics. At 300°C, [NO2] drops from 0.0100 M to 0.00650 M in 100.0 s. The rate constant for the reaction is __________ M-1s-1.
A) 0.096
B) 0.65
C) 0.81
D) 1.2
E) 0.54
A compound decomposes by a first-order process. If 25.0% of the compound decomposes in 60.0 minutes, the half-life of the compound is __________.
A) 65 minutes
B) 120 minutes
C) 145 minutes
D) 180 minutes
E) 198 minutes
The following reaction is second order in [A] and the rate constant is 0.025 M-1s-1:
A → B
The concentration of A was 0.65 M at 33 s. The initial concentration of A was __________ M.
A) 2.4
B) 0.27
C) 0.24
D) 1.4
E) 1.2 × 10-2
The rate constant for this reaction is __________ s-1.
A) 6.9 × 10-2
B) 3.0 × 10-2
C) 14
D) 0.46
E) 4.0 × 102
The concentration of A is __________ M after 40.0 s.
A) 1.3 × 10-2
B) 1.2
C) 0.17
D) 3.5 × 10-4
E) 0.025
The rate constant of a first-order process that has a half-life of 225 s is __________s-1.
A) 0.693
B) 3.08 × 10-3
C) 1.25
D) 12.5
E) 4.44 × 10-3
One difference between first- and second-order reactions is that __________.
A) the half-life of a first-order reaction does not depend on [A]0; the half-life of a second-order reaction does depend on [A]0
B) the rate of both first-order and second-order reactions do not depend on reactant concentrations
C) the rate of a first-order reaction depends on reactant concentrations; the rate of a second-order reaction does not depend on reactant concentrations
D) a first-order reaction can be catalyzed; a second-order reaction cannot be catalyzed
E) None of the above are true.
At elevated temperatures, methylisonitrile (CH3NC) isomerizes to acetonitrile (CH3CN):
CH3NC (g) → CH3CN (g)
The reaction is first order in methylisonitrile. The attached graph shows data for the reaction obtained at 198.9°C.
The rate constant for the reaction is __________ s-1.
A) -1.9 × 104
B) +1.9 × 104
C) -5.2 × 10-5
D) +5.2 × 10-5
E) +6.2
The decomposition of N2O5 in solution in carbon tetrachloride proceeds via the reaction
2N2O5 (soln) → 4NO2 (soln) + O2 (soln)
The reaction is first order and has a rate constant of 4.82 × 10-3 s-1 at 64°C. The rate law for the reaction is rate = __________.
A) k[N2O5]2
C) k[N2O5]
E)2k[N2O5]
As the temperature of a reaction is increased, the rate of the reaction increases because the __________.
A) reactant molecules collide less frequently
B) reactant molecules collide more frequently and with greater energy per collision
C) activation energy is lowered
D) reactant molecules collide less frequently and with greater energy per collision
E) reactant molecules collide more frequently with less energy per collision
The rate of a reaction depends on __________.
A) collision frequency
B) collision energy
C) collision orientation
D) all of the above
E) none of the above
Which energy difference in the energy profile below corresponds to the activation energy for the forward reaction?
A) x
B) y
C) x + y
D) x - y
E) y – x
In the energy profile of a reaction, the species that exists at the maximum on the curve is called the __________.
A) product
B) activated complex
C) activation energy
D) enthalpy of reaction
E) atomic state
In general, as temperature goes up, reaction rate __________.
A) goes up if the reaction is exothermic
B) goes up if the reaction is endothermic
C) goes up regardless of whether the reaction is exothermic or endothermic
D) stays the same regardless of whether the reaction is exothermic or endothermic
E) stays the same if the reaction is first order
The dependence of the rate constant on temperature is studied and the graph below is prepared from the results.
The energy of activation of this reaction is __________ kJ/mol.
A) 160
B) 1.6 × 105
C) 4.4 × 10-7
E) 1.9 × 104
The mechanism for formation of the product X is:
A + B → C + D (slow) B + D → X (fast)
The intermediate reactant in the reaction is __________.
A) A
B) B
C) C
D) D
E) X
Which of the following is true?
A) If we know that a reaction is an elementary reaction, then we know its rate law.
B) The rate-determining step of a reaction is the rate of the fastest elementary step of its mechanism.
C) Since intermediate compounds can be formed, the chemical equations for the elementary reactions in a multistep mechanism do not always have to add to give the chemical equation of the overall process.
D) In a reaction mechanism, an intermediate is identical to an activated complex.
E) All of the above statements are true.
Of the following, __________ will lower the activation energy for a reaction.
A) increasing the concentrations of reactants
B) raising the temperature of the reaction
C) adding a catalyst for the reaction
D) removing products as the reaction proceeds
E) increasing the pressure
A catalyst can increase the rate of a reaction __________.
A) by changing the value of the frequency factor (A)
B) by increasing the overall activation energy (Ea) of the reaction
C) by lowering the activation energy of the reverse reaction
D) by providing an alternative pathway with a lower activation energy
E) All of these are ways that a catalyst might act to increase the rate of reaction.
Nitrogen fixation is a difficult process because __________.
A) there is so little nitrogen in the atmosphere
B) nitrogen exists in the atmosphere primarily as its oxides which are very unreactive
C) nitrogen is very unreactive, largely due to its triple bond
D) of the extreme toxicity of nitrogen
E) of the high polarity of nitrogen molecules preventing them from dissolving in biological fluids, such as those inside cells
Consider the following reaction:
3A → 2B
The average rate of appearance of B is given by Δ[B]/Δt. Comparing the rate of appearance of B and the rate of disappearance of A, we get Δ[B]/Δt = __________ × (-Δ[A]/Δt).
A) -2/3
B) +2/3
C) -3/2
D) +1
E) +3/2
Which substance in the reaction below either appears or disappears the fastest?
A) NH3
B) O2
C) NO2
D) H2O
E) The rates of appearance/disappearance are the same for all of these.
A flask is charged with 0.124 mol of A and allowed to react to form B according to the reaction A(g) →B(g). The following data are obtained for [A] as the reaction proceeds:
The average rate of disappearance of A between 10 s and 20 s is __________ mol/s.
A) 2.2 × 10-3
B) 1.1 × 10-3
C) 4.4 × 10-3
D) 454
E) 9.90 × 10-3
The average rate of appearance of B between 20 s and 30 s is __________ mol/s.
A) +1.5 × 10-3
B) +5.0 × 10-4
C) -1.5 × 10-3
D) +7.3 × 10-3
E) -7.3 × 10-3
A reaction was found to be second order in carbon monoxide concentration. The rate of the reaction __________ if the [CO] is doubled, with everything else kept the same.
A) doubles
B) remains unchanged
C) triples
D) increases by a factor of 4
E) is reduced by a factor of 2
The half-life of a first-order reaction is 13 min. If the initial concentration of reactant is 0.085 M, it takes __________ min for it to decrease to 0.055 M.
A) 8.2
B) 11
C) 3.6
D) 0.048
E) 8.4
A second-order reaction has a half-life of 18 s when the initial concentration of reactant is 0.71 M. The rate constant for this reaction is __________ M-1s-1.
A) 7.8 × 10-2
B) 3.8 × 10-2
C) 2.0 × 10-2
D) 1.3
E) 18
The rate of disappearance of HBr in the gas phase reaction
2HBr (g) → H2 (g) + Br2 (g)
is 0.130 Ms-1 at 150°C. The rate of reaction is __________ Ms-1.
A) 3.85
B) 0.0650
C) 0.0169
D) 0.260
E) 0.0860
Nitrogen dioxide decomposes to nitric oxide and oxygen via the reaction:
In a particular experiment at 300 °C, [NO2] drops from 0.0100 to 0.00550 M in 100 s. The rate of appearance of O2 for this period is __________ M/s.
A) 2.3 × 10-5
B) 4.5 × 10-5
C) 9.0 × 10-5
D) 4.5 × 10-3
E) 9.0 × 10-3
2NOBr (g) → 2 NO (g) + Br2 (g)
is a second-order reaction with a rate constant of 0.80 M-1s-1 at 11°C. If the initial concentration of NOBr is 0.0440 M, the concentration of NOBr after 7.0 seconds is __________.
A) 0.0276 M
B) 0.0324 M
C) 0.0353 M
D) 0.0480 M
E) 0.0402 M
A particular first-order reaction has a rate constant of 1.35 × 102s-1 at 25.0°C. What is the magnitude of k at 95.0°C if Ea = 55.5 kJ/mol?
A) 9.56 × 103
B) 2.85 × 104
C) 576
D) 4.33 × 1087
E) 1.36 × 102
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