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Practice Exam 1A Answers - General Chemistry II | CHEM 113, Exams of Chemistry

Material Type: Exam; Class: General Chemistry II; Subject: Chemistry; University: Colorado State University; Term: Fall 2014;

Typology: Exams

2013/2014

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CHEM113, Fall 2014 – Exam 1A September 18, 2014
Name______________________________
Please mark your exam type (i.e. A or B) on the scantron and write in your student ID
number. Please mark all answers clearly on the provided scantron form. You may wish to
circle your selected answer on this exam (which you may take with you) so that you can compare
your answers with the answers posted on RamCT. There are 25 questions; it is to your
advantage to answer all of them. Each correct answer is worth 4 points.
1.Which of the following statements regarding reaction rates and kinetic molecular theory is
NOT true?
a) Higher concentrations of reactants typically lead to greater reaction rates because of an
increase in the number of effective collisions.
b) The actual dependence on reaction rate on concentration must be determined
experimentally because it depends on the reaction mechanism.
c) At t = 0 the maximum rate is usually observed because only reactant molecules are
present.
d) Collisions between product molecules that reform reactant molecules do not affect the
overall rate of the reaction.
e) As the reaction proceeds, the concentrations of reactants decreases and the rate decreases.
2. The rate of a reaction is found to quadruple when the concentration of both reactants is
doubled, the order of the reaction with respect to each reactant is ___________.
a) first, first
b) second, zero
c) zero, second
d) a and b only
e) all of the above
3. The linear form of the Arrhenius equation is very useful as it allows us to calculate the
___________ from the slope and the _____________ from the y-intercept.
a) frequency factor, activations energy
b) initial concentration, activation energy
c) activation energy, frequency factor
d) activation energy, Boltzmann constant
e) transition state, steric factor
!
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CHEM113, Fall 2014 – Exam 1A September 18, 2014 Name______________________________ Please mark your exam type (i.e. A or B) on the scantron and write in your student ID number. Please mark all answers clearly on the provided scantron form. You may wish to circle your selected answer on this exam (which you may take with you) so that you can compare your answers with the answers posted on RamCT. There are 25 questions; it is to your advantage to answer all of them. Each correct answer is worth 4 points. 1.Which of the following statements regarding reaction rates and kinetic molecular theory is NOT true? a) Higher concentrations of reactants typically lead to greater reaction rates because of an increase in the number of effective collisions. b) The actual dependence on reaction rate on concentration must be determined experimentally because it depends on the reaction mechanism. c) At t = 0 the maximum rate is usually observed because only reactant molecules are present. d) Collisions between product molecules that reform reactant molecules do not affect the overall rate of the reaction. e) As the reaction proceeds, the concentrations of reactants decreases and the rate decreases.

  1. The rate of a reaction is found to quadruple when the concentration of both reactants is doubled, the order of the reaction with respect to each reactant is ___________. a) first, first b) second, zero c) zero, second d) a and b only e) all of the above
  2. The linear form of the Arrhenius equation is very useful as it allows us to calculate the ___________ from the slope and the _____________ from the y - intercept. a) frequency factor, activations energy b) initial concentration, activation energy c) activation energy, frequency factor d) activation energy, Boltzmann constant e) transition state, steric factor
  1. Write the rate of reaction for N 2 O 5 (g) → 2NO 2 (g) + 1/2 O 2 (g) in terms of all species in the balanced equation: a) d[N 2 O 5 ] = - 1 d[NO 2 ] = - 2 d[O 2 ] dt 2 dt dt b) - d[N 2 O 5 ] = 1 d[NO 2 ] = 2 d[O 2 ] dt 2 dt dt c) - d[N 2 O 5 ] = 2 d[NO 2 ] = 1 d[O 2 ] dt dt 2 dt d) d[N 2 O 5 ] = - 2 d[NO 2 ] = - 1 d[O 2 ] dt dt 2 dt e) - d[N 2 O 5 ] = d[NO 2 ] = d[O 2 ] dt dt dt
  2. Given the initial concentration of N 2 O 5 is [N 2 O 5 ]o = 1.24 X 10-^2 moles/L for the reaction in Question 4, if [N 2 O 5 ] = 0.23 X 10-^2 moles/L at t = 55.0 minutes, calculate [NO 2 ] and [O 2 ] at t = 55 minutes. a) [O 2 ] = 0.5 X 10
  • 2 moles/L, [NO 2 ] = 2.0 X 10 - 2 moles/L b) [O 2 ] = 2.0 X 10
  • 2 moles/L, [NO 2 ] = 0.5 X 10
  • 2 moles/L c) [O 2 ] = [NO 2 ] = 0.5 X 10-^2 moles/L d) [O 2 ] = [NO 2 ] = 2.0 X 10-^2 moles/L e) [O 2 ] = [NO 2 ] = [N 2 O 5 ] = 1.24 X 10-^2 moles/L
  1. What is the best way to determine if a particular reaction rate law is first or second order? a) Make a table of concentration values as a function of time b) Take absorption spectra of the reacting system at very short times c) Write out the balanced stoichiometric equation for the reaction d) Determine the reaction half-life e) Plot various functions of the concentration data for the reaction against time and determine which function gives a straight line
  2. For the reaction 3I-( aq ) + H 3 AsO 4 ( aq ) + 2H+( aq ) → I 3 - ( aq ) + H 3 AsO 3 ( aq ) + 2H 2 O( l ), if I-^ is consumed at a rate of 1.2 x 10
  • 4 M /s, H 2 O is produced at a rate of ____________. a) 4.0 x 10
  • 5 M /s b) 8.0 x 10-^5 M /s c) 3.6 x 10-^4 M /s d) 2.4 x 10
  • 4 M /s e) 1.8 x 10
  • 4 M /s
  1. Radioactive decay is a first order reaction (Δ[x]/Δ t = k[x] ), giving the integrated rate law for the decay as ln ([x] 0 /[x] t ) = kt. Derive an expression for the “one-third life” of a radioactive decay. a) t⅓ = 1.1/ k b) t⅓ = 2.2/ k c) t⅓ = 0.231/k d) t⅓ = 0.693/k e) cannot be defined
  2. If the value of ∆Hreact. is - 80 kJ/mol and its activation energy ∆Eact. is 50 kJ/mol, what is the value of the ∆Eactrev (in the reverse direction)? a) - 30 kJ/mol b) 80 kJ/mol c) 30 kJ/mol d) 50 kJ/mol e) 130 kJ/mol
  3. The rate constant for a reaction can be written in an Arrhenius form as k = Ae
    • Ea/RT . Define A and E and give their units. a) A = constant, with no units E = activation energy units depend on forward or reverse reaction b) A = a variable with no units E = a constant with no units c) Need more information to define either A or E d) This expression is not accurate and thus cannot have well defined units for A and E e) A = (steric factor) x (collision frequency), units depend on rate law orders E = activation energy (kJ/mol)
  4. A particular catalyst can bind a reactant through two different transition states, TS 1 or TS 2 , leading to two different intermediates, I 1 and I 2. What is the difference in energy between TS 2 and TS 1 if the reaction proceeds through TS 2 99 times faster than it proceeds through TS 1 at 273 °K (assume A is the same)? a) Ea1 > Ea2; Ea1 - Ea2 = 10.4 x 10 3 J/mol b) Ea1 < Ea2; Ea1 - Ea2 = - 10 .4 x 10^3 J/mol c) Ea1 > Ea2; Ea1 - Ea2 = 1.02 x 10^2 J/mol d) Not enough information to determine e) Ea1 < Ea2; Ea1 - Ea2 = - 1.02 x 10 2 J/mol
  1. If the average rate of reaction for 2O 3 ( g ) → 3O 2 ( g ) is 0.250 M/s over the first 5.50 s, how much oxygen will form during this time? a) 1.38 M b) 4.13 M c) 0.69 M d) 0.25 M e) 0.46 M
  2. Which of the following is true of a catalyzed reaction? a) a catalyzed reaction will involve more elementary steps than the uncatalyzed reaction b) catalysts lower the Ea for a reaction, making the reaction faster c) catalysts lower the ΔH for a reaction, making the reaction more favorable d) a and b only e) all of the above
  3. Determine the overall order of reaction for CO( g ) + Cl 2 ( g ) → COCl 2 ( g ) from the following data: a) one-half b) first c) second d) third e) three-halves
  4. One can relate the rate of reaction through collision theory and the kinetic theory of gases to which factors: a) Fraction of collision with proper energy and molecular orientation b) Total number of collisions with the right energy c) Pressure and temperature of gas reactants d) Collision frequency, fraction of collisions with required energy, and molecular orientations e) Nature of the reactants and products and their bonding
  5. The rate constant for a the reaction 2ClO( g ) → Cl 2 ( g ) + O 2 ( g ) is 7.22 x 10 9 L/mol•s at 273 °K. Suppose 0.0250 atm ClO is initially present in a reaction vessel filled with air at STP (1 atm, 273 °K). What is the half-life of the reaction? a) 5.54 x 10-^9 s b) 1.24 x 10-^7 s c) 1.39 x 10
    • 10 s d) 1.81 x 10
    • 10 s e) 8.09 x 10
    • 12 s Experiment 1 2 3 [CO] ( M ) 1. 000 0. 100 0. 100 [Cl 2 ] ( M ) 0. 100 0. 100 1. 000 Rate ( M **/s)
  6. 29 x 10 -**^29 1. 30 x 10 -^30 1. 30 x 10 -^28
  1. For the reaction SO 2 Cl 2 (g) → SO 2 (g) + Cl 2 (g) the following data apply: Determine rate law and rate constant. a) Zero order, k = 2.20 X 10-^5 (moles/L)s b) Second order, k = 4.40 X 10
    • 5 (moles/L) 2 s - 1 c) First order, k = 2.20 X 10
    • 5 s - 1 d) First order, k = 1.10 X 10
    • 5 (moles/L) 2 s - 1 e) First order, k = 2.20 X 10-^5 (L/moles) s-^1
  2. The reaction Hg 22 + (aq) + Tl^3 + (aq) → 2Hg^2 + (aq) + Tl+ (aq) has a measured rate of reaction (law) = k [Hg 2 2+ ][Tl 3+ ][Hg 2 + ] - 1 A proposed mechanism is
  3. Hg 2 2 + (aq) ⇔ Hg 2+ (aq) + Hg (s) (fast equilibrium)
  4. Hg (s) + Tl^3 + (aq) → Hg2+ (aq) + Tl+ (aq) (slow) Is the mechanism correct and what is the value of the final k? a. Yes, k = k 1 k 2 / k- 1 b. No c. Cannot determine with given data d. Yes, k = k- 1 / k 1 k 2 e. Yes, k = k 2 END OF EXAM 1 Experiment 1 2 3 [SO 2 Cl 2 ] ( M ) 0. 74 1. 25 1. 86 Rate ( M /s) 1. 63 x 10 -^5 2. 75 x 10 -^5 4. 09 x 10 -^5