Chem 2425

30 Questions | By Ochiengj | Last updated: Feb 13, 2013 | Total Attempts: 216

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Questions and Answers

1.

1. If 50.0 g of benzene, C₆H₆, at 25.0⁰C absorbs 2.71 kJ of energy in the form of heat, what is the final temperature of the benzene? The specific heat of benzene is 1.72 J/g·⁰C.
- A.
  
  25.00C
- B.
  
  31.50C
- C.
  
  56.50C
- D.
  
  32.30C
- E.
  
  57.30C
2.

2. If 495 J is required to change the temperature of 12.7 g of sodium chloride from 75.0⁰C to 135 ⁰C, what is the specific heat of sodium chloride?
- A.
  
  0.866 J/g·0C
- B.
  
  2.60 J/g·0C
- C.
  
  0.650 J/g·0C
- D.
  
  1.15 J/g·0C
- E.
  
  2.83 × 105 J/g·0C
3.

3. Water has a specific heat of 4.18 J/g · ⁰C. If 35.0 g of water at 98.8 ⁰C loses 4.94 kJ of heat, what is the final temperature of the water?
- A.
  
  32.00C
- B.
  
  46.20C
- C.
  
  47.20C
- D.
  
  57.20C
- E.
  
  65.0C
4.

4. When 66.0 g of an unknown metal at 28.5⁰C is placed in 83.0 g H₂O at 78.5⁰C, the water temperature decreases to 75.9⁰C. What is the specific heat capacity of the metal? The specific heat capacity of water is 4.184 J/g⁰C.
- A.
  
  0.055 J/g· 0C
- B.
  
  0.29 J/g · 0C
- C.
  
  0.69 J/g · 0C
- D.
  
  0.18 J/g · 0C
- E.
  
  2.6 J/g · 0C
5.

5. A coffee-cup calorimeter contains 10.0 g of water at 59.00⁰C. If 3.00 g gold at 15.20 ⁰C is placed in the calorimeter, what is the final temperature of the water in the calorimeter? The specific heat of water is 4.18 J/g ·⁰C; the specific heat of gold is 0.128 J/g ·⁰C.
- A.
  
  55.37 C
- B.
  
  58.60 C
- C.
  
  59.40 C
- D.
  
  60.80 C
- E.
  
  64.19 C
6.

6. When 10.0 g KOH is dissolved in 100.0 g of water in a coffee-cup calorimeter, the temperature rises from 25.18 ⁰C to 47.53 ⁰C. What is the enthalpy change per gram of KOH dissolved in the water? Assume that the solution has a specific heat capacity of 4.18 J/g⁰C.
- A.
  
  –116 J/g
- B.
  
  –934 J/g
- C.
  
  –1.03 × 103 J/g
- D.
  
  –2.19 × 103 J/g
- E.
  
  –1.03 × 104 J/g
7.

7. 10.0 g of ice at 0.00 ⁰C is mixed with 25.0 g of water at 35.00⁰C in a coffee-cup calorimeter. What is the final temperature of the mixture? The specific heat of water is 4.18 J/g ⁰C; the heat of fusion of water is 333 J/g.

Discuss
- A.
  
  0.00 0C
- B.
  
  2.24 0C
- C.
  
  5.22 0C
- D.
  
  25.0 0C
- E.
  
  47.8 0C
8.

8. All of the following statements are true EXCEPT
- A.
  
  Hess' law states that ΔH for an overall reaction is the sum of the ΔH values for the individual equations.
- B.
  
  The molar enthalpy of formation of a compound is equal to the enthalpy change when one mole of the compound is formed from elements.
- C.
  
  A reaction with a negative enthalpy is exothermic.
- D.
  
  The enthalpy of formation of an element in its most stable state is equal to zero.
- E.
  
  The sum of the enthalpies of formation of the products in a chemical reaction is defined as the enthalpy of reaction.
9.

9. Determine the heat of reaction for the combustion of ammonia, 4NH₃(g) + 7O₂(g) → 4NO₂(g) + 6H₂O(l) using molar enthalpies of formation. NH3(g) –45.9 NO2(g) +33.1 H2O(l) –285.8
- A.
  
  +30.24 kJ
- B.
  
  –206.9 kJ
- C.
  
  –298.6 kJ
- D.
  
  –1398.8 kJ
- E.
  
  –1663.6 kJ
10.

10. The standard molar enthalpy of formation of NH₃(g) is –45.9 kJ/mol. What is the enthalpy change if 9.51 g N₂(g) and 1.96 g H₂(g) react to produce NH₃(g)?
- A.
  
  –10.3 kJ
- B.
  
  –20.7 kJ
- C.
  
  –29.8 kJ
- D.
  
  –43.7 kJ
- E.
  
  –65.6 kJ
11.

11. For the reaction below relate the rate of disappearance of hydrogen to the rate of formation of ammonia. N₂(g) + 3H₂(g) → 2NH₃(g)
- A.
  
  A: +
- B.
  
  B: 3
- C.
  
  C: 1/2
- D.
  
  D: -1/3
- E.
  
  E: -
12.

12. The rate of reaction for the formation of carbon monoxide is measured at 1.24 mol/L·hr. What is the rate of formation of carbon monoxide in units of mol/L·s? CH₃CHO(g) → CH₄(g) + CO(g)
- A.
  
  3.44 × 10-4 mol/L·s
- B.
  
  2.07 × 102 mol/L·s
- C.
  
  1.24 mol/L·s
- D.
  
  74.4 mol/L·s
- E.
  
  4.64 × 103 mol/L·s
13.

13. For the reaction below, if the rate of appearance of Br₂ is 0.180 mol/L·s, what is the rate of disappearance of NOBr? 2NOBr(g) → 2NO(g) + Br₂(g)

Discuss
- A.
  
  –0.360 mol/L·s
- B.
  
  –0.090 mol/L·s
- C.
  
  0.090 mol/L·s
- D.
  
  0.180 mol/L·s
- E.
  
  0.360 mol/L·s
14.

14. Dinitrogen pentaoxide decomposes to nitrogen dioxide and oxygen according to the following balanced chemical equation and rate expression. 2N₂O₅(g) → 4NO₂(g) + O₂(g) rate = k[N₂O₅] What is the overall reaction order?
- A.
  
  0
- B.
  
  1
- C.
  
  2
- D.
  
  5
- E.
  
  7
15.

The initial rates method was used to study the reaction below. A + 3B =2C [A] (mol/L) [B] (mol/L) -D[A]/Dt (mol/L×s) 0.210 0.150 3.41 x 10^3 0.210 0.300 1.36 x 10^2 0.420 0.300 2.73 x 10^-2
- A.
  
  Rate = 0.515[A] x [B]
- B.
  
  Rate = 0.515[A]^2 x [B]
- C.
  
  Rate = 0.721[A]^2 x [B]
- D.
  
  Rate = 0.721[A] x [B]^2
- E.
  
  Rate = 0.721[A]^2 x [B]^2
16.

16. The initial rates method was used to study the reaction below. 2A + B + C → D + E [A] (mol/L) [B] (mol/L) [C] (mol/L) Δ[D]/Δt (mol/L·s) 0.150 0.250 0.300 1.47 × 10^6 0.150 0.125 0.300 3.68 × 10^7 0.150 0.250 0.600 2.94 × 10^6 0.300 0.125 0.300 7.35 × 10^7
- A.
  
  Rate = 8.71 × 104[A]2 × [B] × [C]
- B.
  
  Rate = 5.23 × 104[A] × [B]2 × [C]
- C.
  
  Rate = 2.90 × 103[A]2 × [B] × [C]2
- D.
  
  Rate = 8.71 × 104[A] × [B] × [C]2
17.

17. The rate constant of a first-order decomposition reaction is 0.0147 s^–1. If the initial concentration of reactant is 0.178 M, what is the concentration of reactant after 30.0 seconds?
- A.
  
  8.72 × 105 M
- B.
  
  0.0645 M
- C.
  
  0.115 M
- D.
  
  0.0785 M
- E.
  
  0.643 M
18.

18. The rate constant for the decomposition of cyclobutane is 2.08 × 10^-2 s^-1 at high temperatures. C₄H₈(g) → 2C₂H₄(g) How many seconds are required for an initial concentration of 0.100 M C₄H₈(g) to decrease to 0.0450 M?
- A.
  
  0.00114 s
- B.
  
  1.07 s
- C.
  
  2.64 s
- D.
  
  38.4 s
- E.
  
  874 s
19.

19. The reaction A → B follows first-order kinetics with a half-life of 21.7 hours. If the concentration of A is 0.023 M after 48.0 hours, what is the initial concentration of A?

Discuss
- A.
  
  0.0050 M
- B.
  
  0.051 M
- C.
  
  0.51 M
- D.
  
  0.11 M
- E.
  
  2.0 × 102 M
20.

20. For the first-order reaction below, the concentration of product B after 24.2 seconds is 0.322 M. If k = 8.75 × 10^-2 s^-1, what was the initial concentration of A? A → 2B rate = k[A]

Discuss
- A.
  
  0.0341 M
- B.
  
  0.183 M
- C.
  
  1.34 M
- D.
  
  2.68 M
- E.
  
  29.3 M
21.

21. For the second-order reaction below, the rate constant of the reaction is 9.4 × 10^–3 M^–1s^–1. How long (in seconds) is required to decrease the concentration of A from 2.16 M to 0.40 M? 2A → B rate = k[A]²

Discuss
- A.
  
  2.0 × 10^1 s
- B.
  
  7.8 × 10^1 s
- C.
  
  1.8 × 10^2 s
- D.
  
  1.9 × 10^2 s
- E.
  
  2.2 × 10^2 s
22.

22. For the first-order reaction below, the initial concentration of A is 0.80 M. What is the half-life of the reaction if the concentration of A decreases to 0.10 M in 54 seconds? A → B rate = k[A]
- A.
  
  18 s
- B.
  
  24 s
- C.
  
  36 s
- D.
  
  48 s
- E.
  
  51 s
23.

Which of the following statements is/are CORRECT? 1. Product concentrations appear in the numerator of an equilibrium constant expression. 2. A reaction favors the formation of products if K >> 1. 3. Stoichiometric coefficients are used as exponents in an equilibrium constant expression.
- A.
  
  1 only
- B.
  
  2 only
- C.
  
  3 only
- D.
  
  2 and 3
- E.
  
  1, 2, and 3
24.

What is the correct equilibrium constant expression for the following reaction? CO₂(g) + 2H₂O(g) CH₄(g) + 2O₂(g) a. b. c. d.
- A.
  
  A
- B.
  
  B
- C.
  
  C
- D.
  
  D
25.

25. Write a balanced chemical equation which corresponds to the following equilibrium constant expression.
- A.
  
  1/2N2(g) + 3/2H2(g) = NH3(g)
- B.
  
  N2(g) + 3 H2(g) = 2NH3(g)
- C.
  
  2NH3(g) = N2(g) + 3H2(g)
- D.
  
  NH3(g) = 1/2N2(g) + 3/2H2(g)
- E.
  
  2N2(g) + 6H2(g) = 4NH3(g)

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