A catalyst alters the rate of a chemical reaction by:
A) always providing a surface on which molecules react
B) changing the products formed in the reaction
C) inducing an alternate pathway for the reaction with generallylower activation energy
D) changing the frequency of collisions between molecules
ANSWER: C
Choose the INCORRECT answer. The rate of a chemical reaction:
A) usually is increased when the concentration of one of the reactants is increased
B) is dependent on temperature
C) may be inhibited sometimes by certain catalytic agents
D) will be very rapid if the activation energy is large
ANSWER: D
If a reaction is first order with a rate constant of 5.48 x 10-2 sec-1, how long is required for 3/4 of the initial concentration of reactant to be used up?
A) 25.3 sec
B) 36.5 sec
C) 6.3 sec
D) 18.2 sec
E) none of these
ANSWER: A
The rate constant at 160 oC for the first order decomposition of ore is 0.032/min. The half-life of the reaction is:
A) 62.5 sec
B) 31.25 sec
C) 5000 sec
D) 111 sec
E) none of these
ANSWER: E
A reaction is first order. If its initial rate is 0.0200 M/sec and 25.0 days later its reaction is 6.25 x 10-4 m/sec, then its half-life is:
A) 12.5 days
B) 5.0 days
C) 25.0 days
D) 50.0 days
E) none of these
ANSWER: B
For 2NO + O2 --> 2NO2 , initial rate data are:
| [NO] | 0.010 | 0.010 | 0.030 M |
| [O2 ] | 0.010 | 0.020 | 0.020 M |
| rate | 2.5 | 5.0 | 45.0 mM/sec |
The rate law is Rate = k[O2 ]y and
A) x = 1 y = 2
B) x = 2 y = 1
C) x = 1 y = 1
D) x = 2 y = 2
E) none of these
ANSWER: B
A and B are mixed and the reaction is timed until a color change occurs. The data are:
| [A] | 0.100 | 0.050 | 0.100M |
| [B] | 0.140 | 0.140 | 0.070M |
| time | 25 sec | 50 sec | 100 sec |
The order of the reaction in terms of [A] is:
A) second
B) half
C) zero
D) first
E) none of these
ANSWER: D
For the reaction 2HgCl2 + C2O42- --> products, data are:
| [HgCl2 ], M | 0.0836 | 0.0836 | 0.0418 |
| [C2O42- ] ,M | 0.202 | 0.404 | 0.404 |
| Init. rate, M/hr | 0.26 | 1.04 | 0.53 |
The rate law is Rate = [HgCl ] x [C2O42-] y . Thus
A) x = 2 y = 1
B) x = 2 y = 2
C) x = 1 y = 2
D) x = 1 y = 1
E) none of these
ANSWER: C
The correct units of the specific rate constant for a zero order reaction are:
A) L/mol-sec
B) sec-1
C) sec
D) L2 /mol2 .sec
E) none of these
ANSWER: E
If the half-life of a reaction depends on the concentration of the reactant, then the reaction cannot be __________ order.
A) second
B) zero
C) first
D) third
E) none of these
ANSWER: C
The reaction has the rate law Rate = k[A][B]2. Which will cause the rate to increase the most?
A) doubling [A]
B) lowering temperature
C) tripling [B]
D) quadrupling [A]
E) doubling [B]
ANSWER: C
The reaction 2 H2 + NO ---> H2O + 1/2 N2 is first order in H2 and second order in NO. The rate law is:
A) k[H2]2 [NO]
B) k[H2][NO]2
C) k[H2]
D) k[H2][NO]
E) none of these
ANSWER: B
For a reaction Rate = k[A][B]2, what factor will NOT change k?
A) raising temperature
B) adding inhibitor
C) increasing [A]
D) adding catalyst
E) none of these
ANSWER: C
A variable that has NO EFFECT on reaction rate is:
A) energy of activation
B) temperature
C) catalyst
D) concentration
E) none of these
ANSWER: E
What is the main difference between a Pt catalyst and an enzyme catalyst?
ANSWER: enzyme has greater substrate specificity
What is the order of reaction for the following reaction. Rate = k[A]-1/2[B]1/2 ?
ANSWER: zero order overall
Substance A decomposes by a first-order reaction. Starting initially with [A] = 2.00 M, after 150 min [A] = 0.50 M. For this reaction what is t1/2 ?
ANSWER: 75.0 min
For the above reaction, what is k?
ANSWER: 9.24 x 10-3 min-1
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In the first order reaction A ---> products, [A] = 0.400 M initially and 0.250 M after 15.0 min.
What is the value of the rate constant, k?
ANSWER: 0.034 min-1
What is the half-life of the reaction?
ANSWER: 20.4 min
At what time will [A] = 0.200 M?
ANSWER: 20.4 min
What will [A] be after 175 min.?
ANSWER: 1.04 x 10-3 M
-------------------
The reaction A + B --> C + D is second order in A and zero order in B. The value of k is 0.012 M-1 min-1 . What is the rate of this reaction when [A] = 0.125 M and [B] = 0.435 M?
ANSWER: 1.88 x 10-4 M min-1
Which of the following statements is true about the reaction 2A --->B + C which is first order in A and first order overall:
A) The rate of the reaction will decrease at higher concentrations of B and C.
B) The time required for one half of A to react is directly proportional to the quantity of A.
C) The rate of formation of C is twice the rate of reaction of A.
D) The rate of formation of B is the same as the rate of reaction of A.
E) none of these
ANSWER: E
A catalyst
A) takes part in a reaction and speeds it up
B) appears in the rate equation of a chemical reaction
C) provides an alternate reaction pathway
D) raises the activation energy of a reaction
E) none of the above
ANSWER: C
Define heterogeneous catalysis.
ANSWER: The catalyst is present in a different phase of matter than are the reactants and products.
The rate of a specific chemical reaction is independent of the
concentrations of the reactants. Thus the reaction is
A) first order
B) second order
C) exothermic
D) catalyzed
E) none of these
ANSWER: E
Which of the following does not determine the rate of a reaction?
A) value of DELTA H0
B) activation energy
C) presence of a catalyst
D) temperature of reactants
E) none of these
ANSWER: A
Which of the following lowers the activation energy of a reaction?
A) adding reactants
B) lowering the temperature
C) removing products
D) adding a catalyst
E) raising the temperature
ANSWER: D
If a reaction has a rate equation of rate = k[A][B][C] then it is
A) second order
B) first order
C) third order
D) zero order
E) cannot be determined
ANSWER: C
The first-order reaction A --> Products has a half-life, t1/2, of 55.0 min at 25 oC and 6.8 min at 100 oC. What is the activation energy for this reaction?
ANSWER: 25.8 kJ/mol
Which of the following statements is CORRECT
A) A zero order reaction depends on the concentration ofreactants.
B) A reaction rate cannot be calculated from the collision frequency alone.
C) A commonly stated rule of thumb is that reaction rates triple for a temperature increase of about 10 oC.
D) none of these
ANSWER: B
The first order reaction A---> products has t1/2 = 150 sec. What percent of the sample remains unreacted after 300 sec?
ANSWER: 25%
Define rate law.
ANSWER: An experimentally determined equation that describes how the rate of reaction depends on the concentration of reactants
Define activation energy.
ANSWER: The minimum total kinetic energy that molecules must bring to their collisions for a chemical reaction to occur.
The rate constant for a first-order reaction is k = 0.00073 s-1.
Determine the percent of reactant that has decomposed after 500 s.
ANSWER: 30.6%
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For the reaction A---> products, the following data are obtained:
| First Experiment | Second Experiment | ||
| [A] = 1.512 M | t = 0 min | [A] = 3.024 M | t = 0 min |
| [A] = 1.490 M | t = 1.0 min | [A] = 2.935 M | t = 1.0 min |
| [A] = 1.469 M | t = 2.0 min | [A] = 2.852 M | t = 2.0 min |
Determine the order of the above reaction.
ANSWER: second order
What is the rate constant, k?
ANSWER: 9.62 x 10-3 mol-1 min-1
What is the concentration of [A] in the first experiment after 4.0 min?
ANSWER: 1.429 M
What is the initial rate of the reaction in each experiment?
ANSWER: First experiment = 0.022 mol/min Second experiment = 0.089 mol/min
sources: http://itl.chem.ufl.edu/2041_f97/kinetics_quiz.html
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