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Test 2 Questions for General Chemistry With Qualitative Analysis II | CHM 1046C, Exams of Chemistry

Valencia CollegeChemistry
Prof. Anthony Mellone

Material Type: Exam; Professor: Mellone; Class: Gen Chem with Qual Analysis II; Subject: CHM: Chemistry; University: Valencia Community College; Term: Fall 2007;

Typology: Exams

Pre 2010

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CHM 1046 Fall, 2007
Test 2
Name (print)_________________________
Show your work for complete (and partial) credit. Report your answers to the correct
number of significant figures, and use units where appropriate.
ln([A]t/[A]0) = -kt 1/[A]t = kt + 1/[A]0t½=1/(k[A]0) t½=.693/k
ln(k2/k1) = (Ea/R)[(1/T1) – (1/T2)] k = Ae-Ea/RT
R = .082058L.atm.mol-1K-1 = 8.314J mol-1K-1
1. For the reaction N2(g) + 3H2(g) 2NH3(g), if [NH3(g)]/t. is 0.0088M/s, what is
[H2(g)]/t?
2. Indicate whether the following apply to first and/or second-order reactions. Possible
responses include both first and second-order.
First-order Second-order
a) rate = 7.38 x 10-3M/s
b) k = .0032min-1
c) 1/[A]t = kt + 1/[A]0
d) ln(k2/k1) = (Ea/R)[(1/T1) – (1/T2)]
3. Using the table of initial concentrations and initial rates, determine the rate law and
the value of the rate constant.
[A] (M) [B] (M) [C] (M) Rate (M/min)
.040 .080 .080 2.0 x 10-4
.160 .040 .040 4.0 x 10-4
.040 .040 .040 1.0 x 10-4
.040 .080 .040 2.0 x 10-4
4. For a reaction with k = .0452M-1min-1, how long will it take for the reactant
concentration to drop from 1.22M to 0.610M?
5. For a first-order reaction, the half-life is 7.50min. Starting with an initial reactant
concentration of 2.45M, what will the reactant concentration be after 30.0min?
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CHM 1046 Fall, 2007 Test 2 Name (print)_________________________ Show your work for complete (and partial) credit. Report your answers to the correct number of significant figures, and use units where appropriate. ln([A]t/[A] 0 ) = -kt 1/[A]t = kt + 1/[A] 0 t½=1/(k[A] 0 ) t½=.693/k ln(k 2 /k 1 ) = (Ea/R)[(1/T 1 ) – (1/T 2 )] k = Ae-Ea/RT R = .082058L.atm.mol-1K-1^ = 8.314J mol-1K-

  1. For the reaction N 2 (g) + 3H 2 (g)  2NH 3 (g), if [NH 3 (g)]/t. is 0.0088M/s, what is [H 2 (g)]/t?
  2. Indicate whether the following apply to first and/or second-order reactions. Possible responses include both first and second-order. First-order Second-order a) rate = 7.38 x 10-3M/s b) k = .0032min- c) 1/[A]t = kt + 1/[A] 0 d) ln(k 2 /k 1 ) = (Ea/R)[(1/T 1 ) – (1/T 2 )]
  3. Using the table of initial concentrations and initial rates, determine the rate law and the value of the rate constant. [A] (M) [B] (M) [C] (M) Rate (M/min) .040 .080 .080 2.0 x 10- .160 .040 .040 4.0 x 10- .040 .040 .040 1.0 x 10- .040 .080 .040 2.0 x 10-
  4. For a reaction with k = .0452M-1min-1, how long will it take for the reactant concentration to drop from 1.22M to 0.610M?
  5. For a first-order reaction, the half-life is 7.50min. Starting with an initial reactant concentration of 2.45M, what will the reactant concentration be after 30.0min?
  1. Please explain why increasing the temperature increase the reaction rate. Can you cite a quantitative relationship between the two?
  2. The rate law for the reaction 2NO 2 Cl → 2NO 2 + Cl 2 is first order in NO 2 Cl. Explain why the mechanism cannot be a single step reaction.
  3. At 20.0°C the rate constant for a reaction is 0.125M-1min-1. What will be the value of the rate constant at 32.0°C? The activation energy for the reaction is 57.2kJ/mol For a reaction, the following mechanism was proposed. (Next three questions) Step 1 (fast) 2AB→ A 2 B 2 Step 2 (slow) A 2 B 2 + B → A 2 + B 3 Step 3 (fast) B 3 → B 2 + B
    1. List any reactive intermediates, if any, in the mechanism.
    2. List any catalysts, if any, in the mechanism.
    3. Which one of the following would be an appropriate rate law for the reaction? a) rate = k[AB]^2 b) rate = k[AB]^2 [B] c) rate = k[A 2 B 2 ]^2 [B] d) rate = k[AB]^2 [B]^2 e) rate = k[AB]^2 [B][B 3 ] f) rate = k[AB]^2 [A 2 B 2 ]

2A + B ↔ A 2 B K = 2.3 x 10-4^ (next 2 questions) A 2 B + B ↔ 2AB K = 4.7 x 10-

  1. What is the value of K for the reaction 2A + 2B ↔ 2AB?
  2. What is the value of K for the reaction A 2 B ↔ 2A + B? 19 For the equilibrium CO(g) + 3H 2 (g) ↔ CH 4 (g) + H 2 O(g), ΔH = -206kJ/mol.H = -206kJ/mol. What will be the effect on the position of equilibrium caused by the following? Will the equilibrium shift to the left (in favor of reactants), to the right (in favor of products), or will there be no change? (next 2 questions) shift in equilibrium Change to left to right no change a) Raising the temperature? b) Increasing the total pressure by reducing the volume c)Removing some H 2 O(g)? d) Providing a catalyst?
  3. In the reaction H 2 SO 3 (aq) ↔ H+(aq) + HSO 3 - (aq), K = 1.3 x 10-2. If you wanted to calculate the equilibrium concentrations of all species present after H 2 SO 3 (aq) with a pre-equilibrium concentration of 0.100M reaches equilibrium, you would have to either solve or simplify a quadratic. Show how you would decide whether the quadratic can be simplified or not. Can the quadratic be simplified? Alternatively, solve the quadratic and report the equilibrium concentrations. 5 points extra credit: For the reaction CaC 2 O 4 (s) ↔ Ca+2(aq) + C 2 O 4 -2(aq), K = 2.3 x 10-9. If a solution has [Ca+2] = .0025 and [C 2 O 4 -2] = 1.0 x 10-7M, will a CaC 2 O 4 precipitate form? Show a calculation and interpret the result of the calculation to reach your conclusion.