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Kamis, 06 Desember 2012

Soal-Soal Latihan Termokimia


Thermochemistry
Level 2
Serial Multiple Choice

The next 2 questions relate to the information below:
I. C(s)  +  O2(g)  à  CO2(g)  +  393.3 kJ;     II. CO(g)  +  1/2 O2(g)  à  CO2  +  282.8 kJ.

309. On the basis of the information given in equation II and assuming no change in
    temp­erature  or pressure, one can correctly conclude that
    1) The rate of the reaction is rapid.
    2) The total number of moles of product is the same as the total number of moles
        of reactants.
    3) The reaction is exothermic.
    4) The masses of the product is greater than those of the reactants.
    5) There will be an increase in volume of reactants and products taken together as
         the reaction proceeds.
ANS: 3

310. When 112 grams of CO are used, which of the following occurs?
    1) 1.0 mole of CO2  is produced.
    2) 282.8 kJ of heat are generated.                4) 0.25 mole of CO2  is produced.
    3) 2.0 moles of O2 are consumed.                5) 0.5 mole of O2 is consumed.
ANS: 3
             

The next 2 questions  deal with the following reactions:
I.   Se(s)  +  O2(g)  à  SeO2(g);   DH = -397.9 kJ
 II.  Se(s)  +  1.5 O2(g)  à  SeO3(g);   DH = -297.1 kJ
III. SeO2(g)  +  1/2 O2(g)  à  SeO3(g).

311. The heat of reaction, DH, for reaction III is:
    1) –100.8 kJ;        2) +100.8 kJ;        3) –195.4 kJ;         4) +267.4 kJ;        5) –199.0 kJ.
ANS: 2
      
312. Which statement about these three reactions is false?
    1) In each case, the heat content of the reactants is greater than that of the products.
    2) The first two reactions are exothermic, the third is endothermic.
    3) The potential energy of the reactants of the third reaction is less than the product’s
         potential energy.
      4) The potential energy in the product of the 1st reaction is less than the potential
           energy in the reactants of that reaction.
    5) The kinetic energy in the reactants of the 3rd reaction is greater than the product’s
         kinetic energy.
ANS: 1



The next 3 questions use the equations below:
                I.  C6H6(l)  +  __ O2(g)  à  ___ CO2(g)   +  __ H2O(l)             
               II. 6 C(s)  +  3 H2(g)  +  82.8 kJ  à  C6H6(l)   
              III. C(s)  +  O2(g)  à  CO2(g)  +  393.3 kJ
              IV. H2(g)  +  ½ O2(g)  à  H2O(l)  +   285.8 kJ.

313. The heat of formation, DH, of 1 mole of C6H6(1) is:
    1) –13.8 kJ;       2) –82.8 kJ;       3) +82.8 kJ;        4) –679.1 kJ;       5) +679.1 kJ.
ANS: 3

314. The coefficient for O2 in the combustion of 1 mole of C6H6(1) is
    1) 5;                2) 7;                3) 7.5;                4) 15;                5) 9.
ANS: 3

315. The heat of combustion of one mole C6H6(l) in equation I is obtained by combining
    equations in which of the of ways?
    1) 6 III + 3 IV + II                  3) 6 III - 3 IV + II
    2) –6 IV + 3 IV + II                4) 6 III + 3 IV – II                 5) 6 III + 6 IV + II
ANS: 4


   
The next 2 questions  relate to the following reactions
I. C(s)  +  O2(g)  à  CO2(g)  +  393.3 kJ;     II. CO(g)  +  1/2 O2(g)  à  CO2(g)  +  282.8 kJ.

316. On the basis of the information given in equation II and assuming no change in
    temperature or pressure, one can correctly conclude that
    1) the rate of the reaction is rapid.
    2) the total number of moles of product is the same as the total number of moles
        of reactants.
    3) the reaction is endothermic.
    4) the mass of the product is greater than those of the reactants.
    5) none of these.
ANS: 5

317. When 224 grams of CO are consumed, which of the following occurs?
    1) 1.0 mole of CO2  is produced.
    2) 282.8 kJ of heat are generated.              4) 4.0 moles of O2  are consumed.
    3) 0.25 mole of CO2  is produced.             5) 16.0 grams of O2  are consumed.
ANS: 4



The next 2 questions  relate to these balance equations:  
                   I.  N2  + O2  à  2 NO;   DH =  +180.7 kJ
                  II. N2  +  1/2 O2  à  N2O;   DH =  +81.6 kJ
                 III. 2 N2O  +  O2  à  4 NO.

318. What is the value of DH for reaction III?
    1) +17.6 kJ         2) +81.6 kJ         3) +198.3 kJ         4) +180.7 kJ         5) +120.1 kJ       
ANS: 3 

319. Which of these statements is incorrect?
    1) The direct reaction of elements to form N2O liberates heat.
    2) The potential energy of NO is greater than that of the elements from which it
        was formed.
    3) 90.4 kJ of heat would be needed if 16.0 grams of oxygen react according to
        reaction I.
    4) Some energy possessed by the NO is associated with rotation of the molecules.
    5) Use of a catalyst would not change the DH values given in the equations.
ANS: 1



The next 3 questions  refer to the following reactions:
                          I.  K(s)  + 1/2 Br2(1)  à  KBr(s);   DH = -393.3 kJ
                          II. K(s)   +  1/2 Br2(g)  à  KBr(s);   DH = -415.1 kJ.

320. Which of the following statements about reaction I is wrong?
    1) Heat content of product is less than that of reactants.
    2) For each mole of KBr(s) formed, 393.3 kJ of heat is lost.
    3) The reaction is exothermic.
    4) Potential energy of reactants is less than that of products.
    5) none of these.
ANS: 4

321. The difference between the two heats of reaction, +21.8 kJ, is
    1) the heat required to melt one mole of KBr.
    2) the heat released when two moles of KBr(s) form.
    3) the heat required to vaporize 1/2 mole of liquid Br2.
    4) the heat released in the overall reaction.
    5) probably due to errors in measurement.
ANS: 3

322. The formation of 71.4 grams of KBr(s) in reaction II is accompanied by the release 
      of    1) 21.8 kJ;        2) 124.7 kJ;        3) 249.4 kJ;         4) 1380.7 kJ;        5) 3,550.0 kJ.
ANS: 3                       


The next 3 questions deal with potential energy diagrams below.   These graphs
present two reaction paths for the same overall reaction  A  à  D.








323. The total heat of reaction, DH, for reaction A  à  D By Reaction Path I is 
    1) -10 kJ;             2) +10 kJ;             3) +40 kJ;             4) +50 kJ;             5) -70 kJ.
ANS: 2

324. The activation energy, DH, in reaction step B  à  C for the reaction on  Path I  is
    1) -15 kJ;            2) +20 kJ;           3) +40 kJ;           4) +50 kJ;         5) none of these.
ANS: 2

325. Concerning Reaction Path I, which of the following is false?
    1) At equilibrium both products C and D will be present.
    2) B is considered to be an intermediate product.
    3) The total reaction  A  à  D  is exothermic.
    4) X, Y and Z are points where activated complexes are formed.
    5) The slowest step in the reaction  A  à  D  is probably A  à  B.
ANS: 3



The next 3 questions  refer to the diagram below. 
Substance A reacts to form D by two reaction paths.







326. The overall heat of reaction for Reaction Path II,  A  à  D is:
    1) 70 kJ;               2) 45 kJ;               3) 10 kJ;               4) –5 kJ;               5) –20 kJ.
ANS: 4

327. The activation energy for the reaction step  X  à  D is:
    1) 45 kJ;               2) 35 kJ;               3) 15 kJ;               4) 0 kJ;              5) –15 kJ.
ANS: 2

328. Select the statement that is wrong concerning Reaction Path II:
    1) Removing heat from the reacting system would favor the formation of D.
    2) Product X has a higher heat content than product D.
    3) Reaction  A à  X  is endothermic.
    4) The overall reaction  A à .D  is exothermic.
    5) Activated complexes are represented by points W, X, V and D.
ANS: 5


The next 2 questions  refer to the following reactions:
     I.  S(s)  +  O2(g)  à  SO2(g);    DH = -297.1 kJ.
     II. S(s)  +  1.5 O2(g)  à   SO3(g);    DH = -397.9 kJ.
SO2(g) may be oxidized to SO3(g) as shown in the following equation:
III. SO2(g)  +  0.5 O2(g )  à  SO3(g).

329. The heat of reaction, ΔH, for reaction III is
    1) –100.8 kJ;         2) +100.8 kJ;        3) –195.4 kJ;        4) +267.4 kJ;        5) 328.9 kJ.
ANS: 1

330. Which statement about these three reactions is wrong?
    1) In each case, the heat content of reactants is greater than that of products.
    2) All three reactions are exothermic.
    3) The potential energy of the reactants in the third reaction is less than the P.E.
        of the products.
    4) The P.E. in the product of the 1st  reaction is less than the P.E. in the reactants.
    5) The kinetic energy in the reactants of the 3rd reaction is less than the K.E. in
        the products.
ANS: 3


The next 2 questions  are concerned with factors influencing the rate of reaction.

331. Raising the temperature of a reacting system increases the rate of the reaction,
    but does not increase the:
    1) activation energy.                      
    2) average velocity of the reacting particles.  
    3) vibrational motions within the molecules.
    4) number of collisions.
    5) fraction of reacting particles which possess energies greater than the activation energy.
ANS: 1

332. Reaction rates are also affected by concentration, collision geometry, and the
    presence of a catalyst.  Which is false concerning these factors?
    1) A catalyst lowers the activation energy requirement.
    2) A reaction occurs each time particles of the reactants collide.
    3) Increasing the concentration of reacting particles increases the collision chances.
    4) The slowest reaction involved in a reaction mechanism determines the rate
        of the overall reaction.
    5) none of these.
ANS: 2


The next 3 questions are concerned with the following reactions:
A. H2(g)  +  Cl2(g)  à  2 HC1(g)  +  energy      C. 92U238  à  2He4  +   90Th234  +  energy
B. C12(g)  à  C12(l)  +  energy                          D. Li+(g)  +  Cl-(g)  à  LiCl(s)  +  energy
                                                                            E. none of these equations
333. Of the above reactions, the one involving the smallest amount of energy per mole
    is reaction      1) A;               2) B;               3) C;               4) D;               5) E.
ANS: 2

334. Which one of the following statements is wrong?
    1) Reaction B is a phase change.
    2) In all the reactions above, the product has less enthalpy than the reactant.
    3) All of the reactions are exothermic.
    4) All of the reactions move toward lower potential energy as the reactions occur.
    5) Atoms are conserved in all of the reactions.
ANS: 5

335. The amount of energy stored as nuclear energy changes during the course of
    reaction(s)    1) C only;            2) A & C;          3) B & D;          4) A, C & D;          5) E.
ANS: 1                                                                                                                                               



The next 2 questions  involve the two potential energy diagrams.  The graphs
present two reaction paths for the same overall reaction  A  à  D.






                                                   
                                                   
336.  Comparing Reaction Paths I and II, which one of the following statements is wrong?
    1) Path I could indicate the operation of a catalyst.
    2) Reaction II would probably be a slower reaction.
    3) In both I and II, the forward reaction proceeds simultaneously with the reverse one.
    4) Reaction Path II does not involve the formation of an activated complex.
    5) none of these.
ANS: 4

337. Concerning Reaction Path I, which one of the following statements is false?
    1) At equilibrium both products C and D will be present.
    2) X, Y and Z represent points at which activated complexes are formed.
    3) B is considered to be an intermediate product.
    4) The slowest step in the reaction  A  à  D  is probably  A  à  B.
    5) The total reaction  A  à  D  is exothermic.
ANS: 5



The next 3 questions  refer to the evaporation of water.  Water evaporates spontan­eous,
and has been found by experiment to absorb 2.26 kJ/gram in the process.

338. DH for the reaction  H2O(l)  à  H2O(g),  as calculated from the above data, is:
    1) 2.26 kJ/mole.                          3) 40.6 kJ/mole.
    2) 12.6 kJ/mole.                         4) 75.3 kJ/mole.                     5) 225.9 kJ/mole.
ANS: 3





339. A potential energy diagram that could represent the reaction H2O(l)  à  H2O(g)
    is       1) 1;                 2) 2;                3) 3;                4) 4;                5) 5.
ANS: 5

340. A potential energy diagram that could represent the reaction  H2O(g)  à  H2O(l) 
    is       1) 1;                 2) 2;                3) 3;                4) 4;                5) 5.
ANS: 4


For the next 3 questions:  The following graph illustrates a Potential Energy
diagram for the reaction  Br  +  H2  à .HBr  +  H.







341. Which interval on the graph corresponds to the heat of reaction for the above
     reactions?    1) A                2) B                3) C                4) D                5) B minus A
ANS: 4

342. The activation energy for  HBr  +  H  à  Br  +  H2   is given by
    1) A;                 2) B;                 3) C;                  4) D;                 5) B plus C.                  
ANS: 1

343. Raising the temperature of the system would
    1) decrease only rate of forward reaction.
    2) decrease only rate of reverse reaction.      4) decrease rates of both reverse reactions.
    3) increase only rate of forward reaction.      5) increase rates of both reverse reactions.
ANS: 5


The next 3 questions  relate to the graph which represents two possible
reaction paths for the reaction:  Heat  +  2 NH3(g)  à  N2(g)  +  3 H2(g).








344. The smal1est activation energy shown for the decomposition of  NH3  corresponds
    to the interval labeled
    1) A;                 2) B;                 3) C;                 4) D;                 5) E.
ANS: 2

345. One can correctly conclude from the above graph that the heat of the reaction
    corresponds to the interval labeled
    1) A;                   2) B;               3) C;                  4) D;                 5) E.
ANS: 1

346. The largest activation energy shown for the production of  NH3  corresponds
    to the interval labeled
    1) A;                   2) B;                3) C;                 4) D;                 5) E.
ANS: 4


The next 2 questions  refer to the following curve:





347. Point A on the kinetic energy distribution curve represents the minimum energy
    requirement for the formation of an activated complex.   If the temperature of
    the system is reduced,
    1) point A moves to the left.                          3) point A does not move.
    2) point A moves to the right.                        4) no prediction can be made.
                                                                           5) point A moves only slightly to left.
ANS: 3

348. If a catalyst is introduced into the system
    1) point A moves to the left.                    3) point A does not move.
    2) point A moves to the right.                  4) no prediction can be made.
                                                                     5) point A moves only slightly to right.
ANS: 1


For the next 4 questions:  The potential energy path made by a complex chemical
reaction is illustrated in the diagram below.








349. Which step illustrates a spontaneous endothermic reaction?
    1) 1               2) 2               3) 3               4) 4               5) 5               6) 6               7) 7
ANS: 7

350. Which step does not belong in the reaction mechanism?
    1) 1               2) 2               3) 3               4) 4               5) 5               6) 6               7) 7
ANS: 2

351. Which step will be the rate determining step?
    1) 1               2) 2               3) 3               4) 4               5) 5               6) 6               7) 7
ANS: 5

352. Which step is an exothermic reaction with medium speed?
    1) 1               2) 2               3) 3               4) 4               5) 5               6) 6               7) 7
ANS: 4




For the next 4 questions:  The diagram illustrates the potential energy path made by
a complex chemical reaction.  The reaction mechanism is shown below.

  








 
353. Which step illustrates a spontaneous exothermic reaction?
     1) 1               2) 2               3) 3               4) 4               5) 5               6) 6               7) 7
ANS: 1

354. Which step will be the rate determining step?
    1) 1               2) 2               3) 3               4) 4               5) 5               6) 6               7) 7
ANS: 6

355. Which step does not belong in the reaction mechanism?
    1) 1               2) 2               3) 3               4) 4               5) 5               6) 6               7) 7
ANS: 4

356. Which step is an endothermic reaction with medium speed?
    1) 1               2) 2               3) 3               4) 4               5) 5               6) 6               7) 7
ANS: 3

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