MCQs on Free Energy and Work Function

The energy freely available from the system at a particular set of conditions which can be put into useful work is called free energy. Out of the total energy associated with the system (H) a part of it is random energy which is non-convertible into work. Free energy is a state function and extensive property. In most of the thermodynamic process, neither the energy nor the entropy is held constant. It becomes therefore essential to introduce two new functions involving energy and entropy. Helmholtz free energy contains elastic and surface energy. The effect of normal stress is about three orders of magnitude larger than the effect of elastic energy. Gibbs free energy allows us to determine the amount of chemical energy that a particular reaction can store or release.

1. If the standard free energy change for a reaction is 1.546 kJ/mol at 500oC then the value of the standard equilibrium constant for the reaction is

  1. antilog (0.105)
  2. antilog (-0.105)
  3. antilog (0.241)
  4. antilog (-0.241)

Answer: (b)

2. The standard free energy of formation of NO(g) is

  1. 84.8 kJ/mol
  2. 86.8 kJ/mol
  3. 88.8 kJ/mol
  4. 90.8 kJ/mol

Answer: (b)

3. The term R ln KPo is equal to

  1. – ∆G
  2. – ∆Go
  3. – ∆G/T
  4. – ∆Go/T

Answer: (d)

4. If one gram of kerosene liberates 46.0 kJ of heat when it is burned, to what temperature can 0.25g of kerosene raise the temperature of 75 cm3 of water at 25oC?

  1. 61.6oC
  2. 46.0oC
  3. 66.1oC
  4. 64.0oC

Answer: (a)

5. Which of the following statements regarding entropy is not true?

  1. S (monoclinic) > S (rhombic)
  2. C (diamond) > C (graphite)
  3. H2O(g) > H2O(l)
  4. O3(g) > O2(g)

Answer: (b)

6. Which of the following is expressed to have the largest bond dissociation enthalpy?

  1. HF
  2. HCl
  3. HBr
  4. HI

Answer: (a)

7. During an isothermal expansion of an ideal gas which of the following is true for the gas?

  1. enthalpy decreases
  2. entropy decreases
  3. enthalpy remains constant
  4. entropy remains constant

Answer: (c)

8. For a spontaneous process, the change in Gibbs function is equal to the

  1. the heat content of the system
  2. entropy change of the system
  3. work of expansion
  4. useful work

Answer: (d)

9. Which of the following is an extensive property?

  1. surface area
  2. pressure
  3. molar volume
  4. concentration

Answer: (a)

10. Which of the following is a state function?

  1. q
  2. w
  3. qrev/T
  4. qw

Answer: (c)

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