There heat changes does not Violate the law lo ear 2 Second law of Thermodynamics Suppose a full gas cylinder is connected to an empty one by a tube with a valve. If the Valve is opened / gas flows from the
full to the ampty cylinda until the gas pressure is equal on both sides. 0 closed Initial state E final state open (equilibrian) This expansiun of gas is explained by the second law of thermo- dynamics and a condn of matter called entropy. Entropy- - . Measure of randomness / Disorder of a system. greater the disorder greater the entropy. Sound law states that physical and chemical processes proceed In such a way that the randomness or disorder of the universe (system + surrounding) increases to marimum possible Gas will always expand into an ampty cylinder. Free energy and Reactions First and second laws can be combined in a useful equation, relating the change in energy that can occus in chemical reane and other processar
G= AH- TAS AG change in free energy. DH change in enthalpy (change in heat contnt) T Temperature in Kelvin. ("++273) As 11 is a measure of the proportion of the total energy charge that the change in entropy. energy change - It is the amount of energy in a System available System cannot use in performing work to do useful work at constant temperature and Pressure. Fice energy and entropy changes do. not depend on how the system gets from start to finish Case I Evergonic Case II Endergonic A+B C+D A+B C+D . Keq [c](0] >1.0 Keq [.] [A][B] (A][B] DG" is +ve (Nonispontereous DG" is -ve (spontaneous) move polt usgong tocomplete formed endergonic pat is less the At L during gen tc large +ve change in G negative spontaneous. in entropy AG +ve rean less favourable. When the free energy. change for a KIDD process is determined largfully defined standard condition of lone, pressure, PH Temp it is called standard free energy change (AG) ,DG"= -2.303RTlogK
A+B CHD The rean is now in equiliboun keq - cone of pell rates n both directions are equal Lone of reactant and no forther net changes occure Keg. [c]  in the concs of reartant and pdt. (A][B] rate of realtants L rate of potts 1 law of mass action. if the rean is spontaneous then Keq > Two cases I and 2 In case 2 the rean is less favourable and H requires externa assistance for the completion of the rean. AtB CtD ATP. ADP+Pi The pi is used to make the rean an exerannic On.