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Indicate in which case/cases the spontan...

Indicate in which case/cases the spontaneity of a change is favoured when

A

`DeltaH` `is` `+ve`

B

`DeltaH` `is` `-ve`

C

`DeltaS` `is` `+ve`

D

`DeltaG` `is` `-ve`

Text Solution

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In spontaneous process, `DeltaG =- ve, DeltaH =- ve`, and `DeltaS = +ve`
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Dependence of Spontaneity on Temperature: For a process to be spontaneous , at constant temperature and pressure , there must be decrease in free energy of the system in the direction of the process , i.e. DeltaG_(P.T) lt 0. DeltaG_(P.T) =0 implies the equilibrium condition and DeltaG_(P.T) gt 0 corresponds to non- spontaneity. Gibbs- Helmholtz equation relates the free energy change to the enthalpy and entropy changes of the process as : " "DeltaG_(P.T) = DeltaH-TDeltaS" ""..."(1) The magnitude of DeltaH does not change much with the change in temperature but the entropy factor TDeltaS change appreciably . Thus, spontaneity of a process depends very much on temperature. For endothermic process, both DeltaH and DeltaS are positive . The energy factor, the first factor of equation, opposes the spontaneity whereas entorpy factor favours it. At low temperature the favourable factor TDeltaS will be small and may be less than DeltaH, DeltaG will have positive value indicated the nonspontaneity of the process. On raising temperature , the factor TDeltaS Increases appreciably and when it exceeds DeltaH, DeltaG would become negative and the process would be spontaneous . For an expthermic process, both DeltaH and DeltaS would be negative . In this case the first factor of eq.1 favours the spontaneity whereas the second factor opposes it. At high temperature , when T DeltaS gt DeltaH, DeltaG will have positive value, showing thereby the non-spontaneity fo the process . However , on decreasing temperature , the factor , TDeltaS decreases rapidly and when TDeltaS lt DeltaH, DeltaG becomes negative and the process occurs spontaneously. Thus , an exothermic process may be spontaneous at low temperature and non-spontaneous at high temperature. The enthalpy change for a certain rection at 300 K is -15.0 K cal mol^(-1) . The entropy change under these conditions is -7.2 cal K^(-1)mol^(-1) . The free energy change for the reaction and its spontaneous/ non-spontaneous character will be

CENGAGE CHEMISTRY-THERMODYNAMICS-Exercises (Multiple Correct)
  1. For the adiabatic expansion of an ideal as

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  2. In which of the following entropy increases?

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  3. Which of the following are irreversible processes

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  4. Which of the options give below are correct?

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  5. Which of the following are thermodynamically stable?

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  6. Which of the following affect the heat of reaction?

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  7. Which of the following type of energies are involved in Born Haber's c...

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  8. Which of the following are true about resonance enegry?

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  9. Hess' law is applicable for determination of enthalpy of

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  10. Indicate in which case/cases the spontaneity of a change is favoured w...

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  11. Endothermic reactions, having DeltaS = +ve masy be spontaneous if

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  12. If DeltaH is the enthalpy change and DeltaU the change in internal ene...

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  13. An isolated system is that system in which

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  14. In a reaction, DeltaH and DeltaS both are more than zero. In which of ...

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  15. State the first law of thermodynamics.

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  16. In which reaction(s), DeltaS in negative?

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  17. The heat evolved in the combustion of benzene is given by C(6)H(6) (...

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  18. The heat of neutralization fo a stron acid by a strong base is a const...

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  19. The enthalpy change for the process C("graphite") rarr C(g)is called

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  20. Enthalpy change equal internal energy change when

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