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Which of the reaction is expectd to be s...

Which of the reaction is expectd to be spontaneous at low temperatures and non-spontaneous at high temperatures:

A

Dissociation of `PCl_(5)` to give `PCl_(3)` and `Cl_(2)`

B

Formation of `H_(2)O` from `H_(2)(g)` and `O_(2)(g)`

C

Melting of ice

D

Vaporisation of any volatile liquid

Text Solution

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The correct Answer is:
B
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For a process top be spontaneous, at constant temperature and pressure, there must be decreases in free energy of the system in the direction of the process, i.e. DeltaG_(P.T.)lt0.Delta_(P.T.)=0 implies the equilibrium condition and DeltaG_(P.T.)gt0 corresponding to non-spontaneity. Gibb's Helmholtz equation relates the free energy change to the enthalpy and entropy change of the process as : DeltaG_(P.T.)=DeltaH-TDeltaS ......(i) The magnitude of Delta H does not change much with the change in temperature but the entropy factor TDeltaS changes appreciably. Thus, spontaneity of a process depends very much on temperature. For edothermic proces, both DeltaH "and " DeltaS are positive. The energy factor,the first factor of equation, opposes the spontaneity whereas entropy factor favours it . At low temperature, the favourable factor TDeltaS will be small and may be less than Delta H, DeltaG will have positive value indicating the non-spontaneity 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 exothermic process, both DeltaH " and " DeltaS would be negative. In this case, the first factor of equation(i) favours the spontaneity whereas the second factor opposes it. At high temperature, when TDeltaSgt DeltaH, DeltaG will have positive value, showing thereby the non-spontaneity of the process. However, on decreasing temperature, the factore TDeltaSlt 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 reaction at 300K 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 :

For a process top be spontaneous, at constant temperature and pressure, there must be decreases in free energy of the system in the direction of the process, i.e. DeltaG_(P.T.)lt0.Delta_(P.T.)=0 implies the equilibrium condition and DeltaG_(P.T.)gt0 corresponding to non-spontaneity. Gibb's Helmholtz equation relates the free energy change to the enthalpy and entropy change of the process as : DeltaG_(P.T.)=DeltaH-TDeltaS ......(i) The magnitude of Delta H does not change much with the change in temperature but the entropy factor TDeltaS changes appreciably. Thus, spontaneity of a process depends very much on temperature. For edothermic proces, both DeltaH "and " DeltaS are positive. The energy factor,the first factor of equation, opposes the spontaneity whereas entropy factor favours it . At low temperature, the favourable factor TDeltaS will be small and may be less than Delta H, DeltaG will have positive value indicating the non-spontaneity 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 exothermic process, both DeltaH " and " DeltaS would be negative. In this case, the first factor of equation(i) favours the spontaneity whereas the second factor opposes it. At high temperature, when TDeltaSgt DeltaH, DeltaG will have positive value, showing thereby the non-spontaneity of the process. However, on decreasing temperature, the factore TDeltaSlt 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 298K, 2A+B toC" " Delta H =100 kcal and DeltaS= 0.050 kcal K^(-1) . If DeltaH " and " DeltaS are assumed to be constant over the temperature range, just above what temperature will be reaction become spontaneous?

Knowledge Check

  • For a reaction to be spontaneous at all temperatures

    A
    `Delta G and Delta H` should be ngative
    B
    `Delta H = Delta G=0`
    C
    `Delta G and Delta H` should be positive
    D
    `Delta H lt Delta G`

  • Select the option which is correct regarding true//false of the given stateements: Statements-1: Thermal decomposition of solid CaCO_(3) is expected to be spontaneous as high temperature and non-spontaneous at low temperatures. Statements-2: If the rate law for an acid catalysed reaction is r=K(Reactant)^(1)[Catalyst]^(@) then rate will be independent of presence / absence of catalyst. Statement-3: When water freezes in a glass beaker, volumes of the system increases at constant temperature and hence entropy will also increses.

    A
    All statement are correct
    B
    Only statemen-3 is incorrect
    C
    only statement-1 is correct
    D
    Only statement-2 is incorrect

  • The a reaction to be spontaneous at all temperature

    A
    `DeltaG` and `DeltaH` should be negative
    B
    `DeltaG` for the reaction is zero
    C
    `DeltaG` and `DeltaH` should be positive
    D
    `DeltaH lt DeltaG`

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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. 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?

    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

    For a process top be spontaneous, at constant temperature and pressure, there must be decreases in free energy of the system in the direction of the process, i.e. DeltaG_(P.T.)lt0.Delta_(P.T.)=0 implies the equilibrium condition and DeltaG_(P.T.)gt0 corresponding to non-spontaneity. Gibb's Helmholtz equation relates the free energy change to the enthalpy and entropy change of the process as : DeltaG_(P.T.)=DeltaH-TDeltaS ......(i) The magnitude of Delta H does not change much with the change in temperature but the entropy factor TDeltaS changes appreciably. Thus, spontaneity of a process depends very much on temperature. For edothermic proces, both DeltaH "and " DeltaS are positive. The energy factor,the first factor of equation, opposes the spontaneity whereas entropy factor favours it . At low temperature, the favourable factor TDeltaS will be small and may be less than Delta H, DeltaG will have positive value indicating the non-spontaneity 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 exothermic process, both DeltaH " and " DeltaS would be negative. In this case, the first factor of equation(i) favours the spontaneity whereas the second factor opposes it. At high temperature, when TDeltaSgt DeltaH, DeltaG will have positive value, showing thereby the non-spontaneity of the process. However, on decreasing temperature, the factore TDeltaSlt 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. A reaction has a value of DeltaH =-40 kcal at 400K . Above 400K, the reaction is spontaneous, below this temperature, it is not. The value of DeltaG " and "DeltaS at 400K are respectively:

    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. A reaction has a value of DeltaH =-40 Kcal at 400 k cal mol^(-1) . The reaction is spontaneous, below this temperature , it is not . The values fo DeltaG and DeltaS at 400 k are respectively

    For a process top be spontaneous, at constant temperature and pressure, there must be decreases in free energy of the system in the direction of the process, i.e. DeltaG_(P.T.)lt0.Delta_(P.T.)=0 implies the equilibrium condition and DeltaG_(P.T.)gt0 corresponding to non-spontaneity. Gibb's Helmholtz equation relates the free energy change to the enthalpy and entropy change of the process as : DeltaG_(P.T.)=DeltaH-TDeltaS ......(i) The magnitude of Delta H does not change much with the change in temperature but the entropy factor TDeltaS changes appreciably. Thus, spontaneity of a process depends very much on temperature. For edothermic proces, both DeltaH "and " DeltaS are positive. The energy factor,the first factor of equation, opposes the spontaneity whereas entropy factor favours it . At low temperature, the favourable factor TDeltaS will be small and may be less than Delta H, DeltaG will have positive value indicating the non-spontaneity 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 exothermic process, both DeltaH " and " DeltaS would be negative. In this case, the first factor of equation(i) favours the spontaneity whereas the second factor opposes it. At high temperature, when TDeltaSgt DeltaH, DeltaG will have positive value, showing thereby the non-spontaneity of the process. However, on decreasing temperature, the factore TDeltaSlt 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. When CaCO_(3) is heated to a high temperature, it undergoes decomposition into CaO and CO_(2) whereas it is quite stable at room temperature. The most likely explanation of it, is:

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