Question

Thursday Worksheet #13 ve for the K of this reaction at 325 °Celsius. uestions 1 through 5 deal with the reaction: 2 NO2(g) → N204g). 2 Given the above information, solve for the AGº of the reaction at 325 °Celsius and when AH = -57.2 kJ/mol and AS = -175.5 J/(mol-K) determine whether it is spontaneous initially 0.100 atm of NC K you solve for i . Would this reaction be spontaneous at: all temperatures, low temp.

Answer 1

According to the second law of thermodynamics, the state of entropy of the entire universe, as an isolated system will always increase over time. It also states that the changes in the entropy in the universe can never be negative. In other words, if a reaction is spontaneous if the overall entropy, or disorder increases.
In thermodynamics, the concept of free energy has been introduced to predict the spontaneity or feasibility of a process. Free energy of a system is defined as the maximum amount of energy which available to a system during a process that can be converted into useful work. It is represented by 'G'.
In order to calculate the spontaneity of process, we need to find $\bigtriangleup G$
                                                                  
AG = AH-TAS

where, change in free energy is represented as $\bigtriangleup G$ ; enthalpy as $\bigtriangleup H$ ; change in entropy as $\bigtriangleup S$ and absolute temperature as T.
The equation is called Gibbs Helmholtz equation and is uses to predict the spontaneity of a reaction as follows:-
(1) If $\bigtriangleup G$ is negative, the process is spontaneous
(2) If $\bigtriangleup G$ is positive, the process is non-spontaneous.
(3) If $\bigtriangleup G$ is zero, the process is in equilibrium.

Here, T = 325 degree Celsius
             = (325 + 273) Kelvin
             = 598 Kelvin

     $\bigtriangleup H$ = -57.2 kJ/mol
               = (-57.2 $\times$ $10^{3}$) J/mol
                = -57200 J/mol

      $\bigtriangleup S$ = -175.55 J/(mol-K)

               
AG = AH-TAS

                $\bigtriangleup G$ = -57200 - [598$\times$( -175.55)] J/mol
                        = ( -57200 + 104949) J/mol
                        = + 47749 J/mol
                        = + 47.749 kJ/mol

So, $\bigtriangleup G$ is positive hence reaction is non-spontaneous.