Competitive Exams: Chemistry MCQs (Practice-Test 3 of 31)

  1. For which one of the following reactions does the entropy of the system INCREASE?

    1. NH3 (g) + HCl (g) → NH4Cl (s)

    2. Ag + (aq) + Cl- (aq) → AgCl (s)

    3. 2H2 (g) + O2 (g) → 2H2O (g)

    4. NH3 (g) + H2O (l) → NH4 + (aq) + OH- (aq)

    5. 2H2O2 (l) → 2H2O (l) + O2 (g)

  2. Consider the following characteristics of chemical reactions

    1. spontaneity

    2. maximum amount of work that can be done

    3. speed

    The value of G for a chemical reaction under a given set of conditions provides information about:

    1. 1 only

    2. 2 only

    3. 3 only

    4. 1 and 2

    5. 1, 2 and 3

  3. Consider the following standard reduction potentials, half-reaction Eo, V I3- (aq) + 2e____> 3I- (aq) 0.53 Cr3 + (aq) + e → Cr2 + (aq) -0.41

  4. Calculate Go (in kJ) for the following reaction at 25oC.

  5. Cr2 + (aq) + I3- (aq) → Cr3 + (aq) + I- (aq)

  6. Consider the following reaction, 2SO2 (g) + O2 (g) ⇔ 2SO3 (g), and the following thermochemical data, substance Gfo, kJ/mol, SO2 (g) -300.194, O2 (g) 0.0, SO3 (g) -371.06. Calculate the value of the equilibrium constant for this reaction at 25oC.

    1. N/A

    2. N/A

    3. N/A

    4. N/A

  7. For the dissociation of acetic acid in water at 25oC, CH3COOH (l) + H2O (l) ⇔ H3O + (aq) + CH3COO- (aq), Ho = 284.3 kJ and So = -143.1 J K − 1. Calculate the value of Go (in kJ) for this reaction at equilibrium.

    1. N/A

    2. N/A

    3. N/A

    4. N/A

  8. Consider the carbonylation (i.e.. addition of CO) of methanol, CH3OH, to produce acetic acid, CH3COOH, in a closed system at constant temperature and pressure, CH3OH (g) + CO (g) ⇔ CH3COOH (g), and the following data: Substance Hfo, kJ mol-1So, J mol-1 K − 1, CH3OH (g) -201240, CO (g) -110198, CH3COOH (g) -432283 If the initial concentration of CH3OH (g) is 1.5 M and the initial concentration of CO (g) is 2.0 M, what is the concentration (in M) of CH3OH (g) at equilibrium, at 298 K?

    1. N/A

    2. N/A

    3. N/A

    4. N/A

  9. For which of the following processes does the entropy of the system DECREASE?

    1. Melting of ice.

    2. Dissolving table salt in water.

    3. Decomposition of liquid hydrogen peroxide to produce liquid water and oxygen gas.

    4. Precipitation of silver chloride from a solution containing silver ions and chloride ions.

    5. The entropy of the system increases in all of the above processes.

  10. For a particular chemical reaction, the values for H and S are both positive. Which of the following statements is TRUE about this reaction?

    1. The reaction is spontaneous at any temperature.

    2. The reaction is not spontaneous at any temperature.

    3. The reaction is spontaneous when the temperature is high enough to overcome H.

    4. The reaction is spontaneous when the temperature is low enough to overcome H.

    5. The reaction is spontaneous when the temperature is low enough to overcome S.

  11. For the boiling of methanol, CH3OH (l) → CH3OH (g), Ho = + 38.0 kJ, and So = + 113.0 J/K. Assume that methanol boils at a temperature at which the value of G is equal to zero. Using the values of Ho and So, calculate the temperature (in K) at which methanol boils.

    1. N/A

    2. N/A

    3. N/A

    4. N/A

  12. Which of the following reactions is unfavorable at low temperatures but becomes favorable as the temperature increases?

    1. 2 CO (g) + O2 (g) → CO2 (g); Ho = -566 kJ; So = -173 J/K

    2. 2 H2O (g) → 2 H2 (g) + O2 (g); Ho = 484 kJ; So = 90.0 J/K

    3. 2 N2O (g) → 2 N2 (g) + O2 (g); Ho = -164 kJ; So = 149 J/K

    4. PbCl2 (s) → Pb2 + (aq) + O2 (g); Ho = 23.4 kJ; So = -12.5 J/K

  13. The following reaction is spontaneous as written: Zn (s) + Cu2 + (aq) → Zn2 + (aq) + Cu (s) Which of the following statements is TRUE?

    1. Keq > 1 and Go = 0

    2. Keq > 1 and Go < 0

    3. Keq < 1 and Go < 0

    4. Keq > 1 and Go > 0

    5. Keq < 1 and Go = 0

  14. A spontaneous reaction ALWAYS occurs when:

    1. Ho < 0 and So < 0

    2. Ho > 0 and So < 0

    3. Ho < 0 and So > 0

    4. Ho > 0 and So = 0

    5. Ho > 0 and So > 0

  15. When a reaction is at equilibrium, which of the following statements is TRUE?

    1. G = Go

    2. ln Keq = 0

    3. Go = 0

    4. Q = 0

    5. G = 0