Northrup's Chem 112 Section TTU General Chemistry

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Chem 112 - Quiz 2B - Spring, 1998
Chapter 15: Chemical Thermodynamics and Some Kinetics

1. Which statement is INCORRECT?

a) A process that absorbs energy from its surroundings is called endothermic.
b) In an exothermic reaction the enthalpy of species increases.
c) Energy is the capacity to do work or to transfer heat.
d) Kinetic energy is the energy of motion.
e) Potential energy is the energy that a system possesses by virtue of its position or composition.

2. There are two properties of a reacting system that determine whether a process at constant pressure and temperature can occur spontaneously. These are:

a) kinetic and potential energy change
b) heat and work
c) energy change and enthalpy change
d) enthalpy change and entropy change

3. The two properties in Question 2 can be combined to give a single thermodynamic state property of a system which dictates whether a process can occur spontaneously. This property is the:

a) rate constant
b) free energy change
c) rate law
d) heat content
e) exothermicity

4. Identify the INCORRECT statement:

a) An endothermic process which is spontaneous must have a positive DS.
b) Every naturally occuring spontaneous process is attended with an increase in the entropy of the universe.
c) Every naturally occuring spontaneous process in a system is attended with a decrease in free energy of the system.
d) A process which causes the system entropy to decrease can still be spontaneous if an even larger entropy increase takes place in the surroundings.
e) Every naturally occuring spontaneous process in a system is attended with an increase in entropy of the system.

5. Which process is accompanied by a decrease in entropy of the materials?

a) expansion of a gas into a vacuum
b) solution formation
c) crystal formation
d) thermal equilization between two regions in thermal contact
e) diffusion of solute molecules into a region of low solute concentration

6. How much heat is absorbed in the complete reaction of 3.00 grams of SiO2 with excess carbon in the reaction below? DH° for the reaction as written is +624.7 kJ.

SiO2(g) + 3 C(s) ---> SiC(s) + 2 CO(g)

a) 31.2 kJ
b) 1.13 x 105 kJ
c) 5.06 kJ
d) 1.33 x 104 kJ
e) 366 kJ

7. From the following data at 25°C:

H2(g) + Cl2 ---> 2 HCl(g); DH° = -185 kJ
2 H2(g) + O2(g) ---> 2 H2O(g); DH° = -483.7 kJ

Calculate DH° at 25° for the reaction below:

4 HCl(g) + O2(g) ---> 2 Cl2(g) + 2 H2O(g)

a) +114 kJ
b) +299 kJ
c) -299 kJ
d) -114 kJ
e) -86.8 kJ

8. Given the standard heats of formation for the following compounds, calculate the DH° heat of reaction, for the following reaction:

Fe3O4(s) + CO(g) ---> 3 FeO(s) + CO2(g)

DHf° for Fe3O4 = -1118 kJ
DHf° for CO = -110.5 kJ
DHf° for FeO = -272 kJ
DHf° for CO2 = -393.5 kJ

a) 54 kJ
b) 19 kJ
c) -263 kJ
d) -50 kJ
e) 109 kJ

9. Estimate the temperature where DG = 0 for the following reaction: (Given: DH = -176 kJ and DS = -284.5 J/K) CAUTION: Beware of units.

NH3(g) + HCl(g) ---> NH4Cl(s)

a) 582 K
b) 467 K
c) 619 K
d) 634 K
e) 680 K

10. Of the following factors, which cannot affect the rate of a chemical reaction?

a) all can effect the rate
b) temperature
c) presence of a catalyst
d) concentration of reactants of the forward reaction
e) physical state or state of subdivision of solid reactants

11. Consider the following rate law expression: Rate = k[A]2[B]. Which of the following is NOT TRUE about the reaction having this expression?

a) The reaction is overall third order.
b) The reaction is first order in B.
c) Doubling the concentration of A doubles the rate.
d) The reaction is second order in A.

12. The gas phase reaction A + B ---> C has a reaction rate which is experimentally observed to follow the relationship Rate = k[A]2[B]. If the concentration of A is tripled and the concentration of B is doubled, the reaction rate would be increased by a factor of _____.

a) 9
b) 6
c) 18
d) 12
e) 24

13. Determine the rate-law expression for the reaction below:

2A + B2 + C --> A2B + BC 

	Run #	Initial Rate (M-1s-1)	[A]o	[B2]o
	[C]o
	-----------------------------------------------------
	1	1.6 x 106	1.2 M	1. x 10-2 M	1.0 M
	2	1.6 x 106	2.4 M	1. x 10-2 M	1.0 M
	3	3.2 x 106	1.2 M	2. x 10-2 M	1.0 M
	4	6.4 x 106	1.2 M	1. x 10-2 M	2.0 M

a) Rate = k[A][B2][C]
b) Rate = k[A]2[B2][C]
c) Rate = k[B2]2[C]2
d) Rate = k[B2]2[C]4
e) Rate = k[B2][C]2

KEY

1)b 2)d 3)b 4)e 5)c 6)a 7)d 8)b 9)c 10)a 11)c 12)c 13)e
To send electronic mail to Dr. Northrup ====> snorthrup@tntech.edu, or call 615-372-3421, or come to Foster Hall 219