Northrup's Chem 112 Section TTU General Chemistry

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Chem 112 - Quiz 2A - Spring, 1997
Chapter 15: Chemical Thermodynamics and Some Kinetics

1. Identify the INCORRECT statement below:

a) Potential energy is the energy possessed by virtue of position or composition.
b) Energy is the capacity to do work or transfer heat.
c) In an exothermic reaction the value of H of the species is increasing in going from reactants to products.
d) Energy is neither created or destroyed in ordinary chemical reactions.
e) Kinetic energy is the energy of motion.

2. Identify the INCORRECT statement below:

a) The symbol H refers to the enthalpy, or "heat content" of the system.
b) The DH of a reaction tells one the heat liberated or absorbed under constant pressure reaction conditions.
c) The internal energy change of a system equals the heat absorbed minus the work done by the system.
d) The second law states that DS of a system increases in any spontaneous process.
e) The symbol G refers to the Gibbs' free energy of the system.

3. A calorimeter temperature increases by 0.45 °C when 30 J of energy is added to it by electrical heating. When 0.10 grams of HCl is neutralized in the same calorimeter, the temperature increased by 7.3 °C. What is the DH of neutralization of HCl in units of kJ/mol?

a) -177 kJ/mol
b) 0.486 kJ/mol
c) 1.8 x 102 kJ/mol
d) -486 kJ/mol
e) 177 kJ/mol

4. Given that:

S(s) + O2(g) --> SO2(g); DH = -296.8 kJ/mol
2 SO3(g) --> 2 SO2(g) + O2(g); DH = +197.8 kJ/mol

Determine the enthalpy change of the reaction: 2 S(s) + 3 O2(g) --> 2 SO3(g)

a) -99 kJ/mol
b) 99 kJ/mol
c) 495 kJ/mol
d) -495 kJ/mol
e) -791.4 kJ/mol

5. Use the data in the table to calculate the DH°rxn of the following reaction at 298 K:

HI(g) + ICl(g) --> HCl(g) + I2(g) 

       SPECIES        DH° at 298 K      DG° at 298 K
                           (kJ/mol)             (kJ/mol)
       ------------------------------------------------------
        HCl(g)            -92.31               -95.30
        I2(s)               0                    0
        I2(g)             62.44                19.36
        ICl(g)             17.78                -5.52
        HI(g)              26.5                  1.72

a) -136.6 kJ/mol
b) 110.4 kJ/mol
c) -74.1 kJ/mol
d) 48.0 kJ/mol

6. Using the data in the table, compute the standard entropy change DS° of the sublimation of iodine at 298 K:

I2(s) --> I2(g)

a) -1.4 x 10-1 kJ/mol K
b) -62.44 kJ/mol K
c) -19.36 kJ/mol K
d) +0.1445 kJ/mol K

7. Identify the INCORRECT statement below:

a) In spontaneous changes the universe tends toward a state of greater disorder.
b) The Gibbs free energy of a system is increasing in any spontaneous process going on at constant T and P.
c) The entropy of a pure, perfect crystal at T = 0 K is zero.
d) The entropy of a system can decrease in a spontaneous process, if the surrounding entropy is increasing even more.
e) The expansion of a gas into a vacuum is an example of an increase in entropy.

8. Identify the INCORRECT statement below concerning chemical kinetics:

a) The rate of a chemical reaction changes with time.
b) The rate constant of a reaction generally depends on the concentrations of species.
c) The rate of a chemical reaction is affected by the temperature of the reaction.
d) The rate law of a chemical reaction bears no relationship with the balancing coefficients of the overall reaction.
e) The rate law expresses how the rate varies with concentration of species.

9. The rate law for the iodine clock reaction is given by: Rate = k[IO3- ][I- ]2[H+]2

a) This reaction is first order with respect to IO3- and third order overall.
b) This reaction is second order with respect to I- and 3rd order overall.
c) This reaction is first order with respect to IO3- and fifth order overall.
d) This reaction is third order with respect to H+.

10. Consider the following kinetic data collected at the very beginning of a reaction: 

     Run #    Initial [A]    Initial [B]    Initial Rate of Reaction
               (mol/L)         (mol/L)              (mol/L-s)
     ----------------------------------------------------------------
      1         0.10            0.10                 0.0090
      2         0.20            0.10                 0.036
      3         0.10            0.20                 0.018

Which of the following is an appropriate expression for the rate law and rate constant?

a) Rate = k[A]2[B]; k = 9.0 L2/mol2-s
b) Rate = k[A]2[B]; k = 0.9 L2/mol2-s
c) Rate = k[A]4[B]2; k = 9.0 x 103 L/mol-s
d) Rate = k[A][B]; k = 0.9 L/mol-s

11. In the overall reaction given by: H2(g) + 2 ICl(g) --> I2(g) + 2 HCl(g)

a) the concentration of all species are changing by the same amount at all times.
b) the concentration of HCl increases equally as fast as I2.
c) the concentration of H2 decreases at the same rate as ICl.
d) the concentration of HCl increases twice as fast as I2.

KEY

1)c 2)d 3)a 4)e 5)c 6)d 7)b 8)b 9)c 10)a 11)d
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