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Read the following statements regarding ...

Read the following statements regarding spontaneity of a process and mark the appropriate choice.
(i) When enthalpy factor is absent then randomness factor decides spontaneity of a process.
(ii) When randomness factor is absent then enthalpy factor decides spontaneity of a process.
(iii) When both the factors take place simultaneously, the magnitude of both of factors decide spontaneity of a process.

A

Statements (i) and (ii) are correct and (iii) is incorrect.

B

Statement (iii) is correct, (i) and (ii) are incorrect.

C

Statements (i), (ii) and (iii) are correct.

D

Statements (i), (ii) and (iii) are incorrect.

Text Solution

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The correct Answer is:
C
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Red the following statements regarding spontaneity of a process and mark the appropriate choice.

Which of following factor always increases for spontaneous process

When Delta H and TDeltaS both are negative , then for spontaneous process which option is true?

Assertion (A): The thermodynamic factor which determines the spontaneity of a process is the free energy. For a process to be spontaneous the free energy must be-ve. Reason (R ) : The change in free energy is related to the change in a process must always be positive if its is spontaneous.

Assertion:Spontaneous process is an irreversible process and may be reversed by some external agency. Reason:Decrease in enthalpy is a conrtributory factor for spontaneity.

Assertion (A). Spontaneous process is an irreversible process and may be reversed by some external agency. Reason (R). Decrease in enthalpy is a contributory factor for spontaneity

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

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. For the reaction at 298 K ,2A + B rarr C DeltaH =100 kcal and DeltaS=0.050 kcal K^(-1) . If DeltaH and DeltaS are assumed to be constant over the temperature range, above what temperature will the reaction become spontaneous?

NCERT FINGERTIPS-THERMODYNAMICS-Spontaneity
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  2. What will be the melting point of KCl if enthalpy change for the reac...

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  3. For reversible reaction : X((g))+3Y((g))hArr 2Z((g)), DeltaH=-"40 kJ" ...

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  4. At 373 K, steam and water are in equilibrium and DeltaH=40.98" kJ mol"...

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  5. Match the column I with column II and mark the appropriate choice.

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  6. Read the following statements regarding spontaneity of a process and m...

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  7. Which of the following processes is a non-spontaneous process?

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  8. Which of the following statements regarding Gibb's energy change is co...

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  9. For a reaction to be spontaneous at any temperature, the conditions ar...

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  10. For the reaction given below the value of standard Gibbs free energy o...

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  11. What is the entropy change when 1 mole oxygen gas expands isothermally...

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  12. Mathc the following columns and mark the appropriate choice.

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  13. One word answer is given for the following definitions, Mark the one w...

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  14. In a reaction P+Q rarr R+S, there is no change in entropy, Enthalpy ch...

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  15. For reaction, 2K((g))+L((g))rarr2M((g)),DeltaU^(@)=-"10.5 KJ and "Delt...

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  16. Which of the following statements is not correct ?

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  17. DeltaG is the net energy available to do useful work and is a measure ...

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  18. Dissolution of ammonium chloride in water is an endothermic reaction, ...

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  19. What will be the signs of DeltaH and DeltaS when NaOH is dissolved in ...

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