2nd General Chemistry College Course Pactice Exam

SHOW ALL WORK
Useful numbers: R = 0.08206 L atm/mol K = 8.314 J/mol K
1 atm = 760 torr = 760 mm Hg     

Multiple choice (2 points each)
1. I dissolved some NaCl in pure water, the boiling point was ________?
a) same as pure water
b) higher than pure water
c) lower than pure water
d) none of the above


2. Which change in the system will change drive the equilibrium to the left in the reaction below?
N2O5(g)  NO2(g) + NO3(g)

a) Decrease the amount of NO3
b) Increase the amount of N2O5
c) Increase the pressure
d) Increase the volume


3.   The slowest step in a reaction is called the _______ step?
a) activation
b) elementary
c) rate law
d) rate determining


4.   For the general rate law, rate = k[A]2[B], what will happen to the rate if the concentration of [A] is doubled
a) rate will remain the same
b) rate will double
c) rate will quadruple
d) rate will be halved


5. The reaction A + B  products is third order in A and first order in B.  The overall order for the reaction is:
a) 4
b) 3
c) 2
d) 1


6.  If Kc = 0.11 at 25 C for the reaction N2O4(g)  2 NO2(g), what is Kc' for the reaction 2 NO2(g)  N2O4(g) at 25 C?
a) 9.1
b) 4.5
c) 3.0
d) 0.33


7. A mechanism for a naturally occurring reaction that destroys ozone is
step 1:  O3(g) + HO(g)    HO2(g) + O2(g)
step 2:  HO2(g) + O(g)    HO(g) + O2(g)
Which one represents a catalyst?
a) HO2
b) HO
c) O
d) O3


8.  The elementary  reaction NO2(g) NO(g) + O(g)  is an example of a ________ reaction.
a) unimolecular
b) bimolecular  
c) trimolecular     
d) tetramolecular

9. Which change in the system will change drive the equilibrium to the right in the exothermic reaction below?
FeO(s)+CO(g)  Fe(s) + CO2(g)
a)  Add FeO
b)  Add CO
c)  Add CO2
d)  Add Fe


10.   Which would be the most soluble in water
a) butane (C4H10)
b) methanol (CH3OH)
c) methylamine (CH3NH2)
d) hydrogen peroxide (H2O2)


11. The half life for a second order reaction is  
a) independent on concentration  
b) dependent of concentration  
c) dependent on the square of the concentration
d) independent of the rate constant


12.  What is the overall reaction order represented by the rate law: Rate = k[I2][NO]2?
a) zero
b) first
c) second
d) third


13.  To make a 2.00 M solution, one could take 2.00 moles of solute and add
a) 1.00 L of solvent
b) 1.00 kg of solvent
c) enough solvent to make 1.00 L of solution
d) enough solvent to make 1.00 kg of solution


14.  Which of the following statements about a catalyst is true?
a) A catalyst changes the position of the equilibrium in a reaction
b) A catalyst provides a lower energy pathway for a reaction
c) A catalyst is consumed in a chemical reaction
d) A catalyst increases the temperature of the reaction


15.  What are the units for the general rate law: rate = k [A]2[B]?
a) s-1
b) M-1s-1
c) M-2s-1
d) M-3s-1

Multiple choice 5 points each
16. At a given temperature the vapor pressures of benzene and toluene are 183 mm Hg and 59.2 mm Hg respectively.  Calculate the total vapor pressure over a solution of benzene and toluene with Xbenzene = 0.600
a) 108 mm Hg
b) 121 mm Hg
c) 133 mm Hg
d) 242 mm Hg


17. What would be the expected freezing point of a 0.15 m solution of MgCl2 and water.  Kf for water is 1.86 C kg/mol?
a) - 0.84 C
b) 0.84 C
c) - 0.28 C
d) 0.28 C



18. Calculate the equilibrium constant, Kp, for 2 NO(g) + Cl2  2NOCl(g) when the partial pressure at equilibrium for each of the three gases is 0.095 atm NO, 0.171 atm Cl2 and 0.28 atm for NOCl
a) 0.020
b) 4.8
c)  17
d) 51


19. The following reaction is first order: C2H6  2 CH3. If the initial rate constant = 5.5 x 10-4 s-1 at 1000 K.  How long will it take for the initial  [C2H6] = 0.35 M to fall to 0.10 M?
a) 2.3 x 103 s
b) 5.2 x 102 s
c) 2.3 x 10-3 s
d) 1.3 x 104 s


20. Calculate the mole fraction of Ca2+ in water, when the molality is 3.25 m of CaCl2 in water.
a) 3.25
b) 0.50
c) 0.33
d) 0.050



Watch significant figures!
SHOW ALL WORK!
Problems:
21. Calculate Kc at 427 C for the reaction: CH4(g) + H2O(g)  CO2(g) + 3 H2(g),  if Kp = 9.48 at 427 C (8 points)


22. My cat has a solution containing 0.500 g of a polypeptide in 1.00 L of water, which has an osmotic pressure of 4.74 torr at 27 C.   What is the approximate molecular weight of the cat's polypeptide? (10 points)


23. Given the rate constants for the reaction 2HI(g)  H2(g) + I2(g) are 1.57 x10-3 L/mol s at 700 C and 1.19 x 10-4 L/mol s at 600 C, calculate the activation energy.  (10 points)



24.  Draw the potential energy diagram for an endothermic reaction.  Be sure to label axis, reactants, products and Ea. (7 points)



25.) A 2.000 L flask is filled with 2.000 mol of H2 and 2.000 mol of I2 at 448 C.  The value of the equilibrium concentration, Kc, for the reaction: H2(g) + I2(g)  2HI(g)  at 448 C is 50.5.  What are the concentrations of H2, I2, and HI in the flask at equilibrium? (10 points)

Attached file(s):

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