Spontaneity Of A Process And Enthalpy Change

Enthalpy And Enthalpy Change

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.

Statement: The thermodynamics functions which determines the spontaneity of a process is the free energy. For a process to be spontaneous, the change in free energy must be negative. Explanation:The change in free energy is related to the change in enthalpy and change in entropy. the change in entropy for a process must be always positive if it is spontaneous.

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.

Gibbs-Helmoholtz equation relates the free energy change to the enthalpy and entropy changes of the process as (DeltaG)_(PT) = DeltaH - T DeltaS The magnitude of DeltaH does not change much with the change in temperature but the enrgy factor T DeltaS changes appreciably. Thus, spontaneity of a process depends very much on temperature. The enthalpy change for a certain reaction at 300K is -15.0 kcal mol^(-1) . The entropy change under these conditions is -7.2 cal K^(-) mol^(-1) . The free enegry change for the reaction and its spontaneous//nonspontaneous character will be

Gibbs-Helmoholtz equation relates the free energy change to the enthalpy and entropy changes of the process as (DeltaG)_(PT) = DeltaH - T DeltaS The magnitude of DeltaH does not change much with the change in temperature but the enrgy factor T DeltaS changes appreciably. Thus, spontaneity of a process depends very much on temperature. For the reaction at 298K, 2A +B rarr C Deltah = 100 kcal and DeltaS = 0.020 kcla K^(-1) . If DeltaH and DeltaS are assumed to be constant over the temperature range, at what temperature will the reaction become spontaneous?

Gibbs-Helmoholtz equation relates the free energy change to the enthalpy and entropy changes of the process as (DeltaG)_(PT) = DeltaH - T DeltaS The magnitude of DeltaH does not change much with the change in temperature but the enrgy factor T DeltaS changes appreciably. Thus, spontaneity of a process depends very much on temperature. A reaction has value of DeltaH - 20 kcal at 200K , the reaction is spontaneous, below this temperature, it is not. the values DeltaG and DeltaS at 400K 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. 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 :