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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

`DeltaG` is +ve

B

`DeltaH` is -ve

C

`DeltaS` is +ve

D

`DeltaS` is `-ve`

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The correct Answer is:
B, C, D
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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

FIITJEE-THERMODYNAMICS AND THERMOCHEMISTRY -ASSIGNMENT PROBLEMS (OBJECTIVE) LEVEL-II
  1. Which of the following conditions will apply to the conversion of ice ...

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  2. The following is (are) endothermic reaction (s)

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  3. For the adiabatic expansion of an ideal gas

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  4. In which of the following entropy increases?

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

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

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  7. For gaseous reactions, if DeltaH is the change in enthalpy and DeltaU ...

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  8. Which of the following statements is/are incorrect?

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  9. The open system (s) is (are) which :

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  10. In a reaction DeltaH and DeltaS both are more than zero. In which of t...

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  11. If W is work doone by the system (-ve), the mathematical representatio...

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

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

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  14. The heat of neutralization of a strong acid by a strong base is a cons...

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  15. The enthalpy of formation of UF(g) is 22 kcal "mol"^(-1) and that U(g)...

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  16. When a liquid solidifies, generally there is

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  17. Which of the following statement(s) is/are correct?

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  18. Methanol can be synthesised in the gas phase from methane and steam as...

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  19. Methanol can be synthesised in the gas phase from methane and steam as...

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  20. Methanol can be synthesised in the gas phase from methane and steam as...

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