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    Thermodynamics
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    Define thermodynamics.

    The branch of science which deals with the study of different forms of energy and the quantitative relationships between them is known as thermodynamics.

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    (a) What are Exergonic and Endergonic reactions?
    (b) Given that the standard heat of formation of NH3(g) as represented by the equation
    1 half straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 over 2 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space NH subscript 3 left parenthesis straight g right parenthesis
    is – 46.191 kJ. The standard entropies of N2(g), H2(g) and NH3(g) are 191.62, 130.12 and 193.3 JK–1 mol–1 respectively. Calculate the standard free energy of formation (∆G0) for NH3. Is the reaction feasible?

    (a) A reaction which is accompanied by the decrease of free energy is called exergonic reaction. All spontaneous processes are exergonic. It means in an exoergic reaction, ∆G is less than zero i.e. ∆G is negative.
    A reaction Which is accompanied by the increase of free energy is called endergonic reaction. All non-spontaneous processes are endergonic. It means an endergonic reaction ∆G is greater than zero i.e. ∆G is positive.

    (b) Here,

    We know,

       
    Also,


    Substituting the values, we have,

    Since the value of     ∆rG° is negative, the reaction is feasible.
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    (i) What are the limitations of criterion for randomness?
    (ii) Calculate the standard free energy of formation of straight H subscript 2 straight O subscript 2.The free change for the reaction.
    straight H subscript 2 straight O subscript 2 space space rightwards arrow space space space straight H subscript 2 straight O space plus space 1 half straight O subscript 2 space space is space space space space space space space space increment straight G to the power of 0 space equals space minus 125.10 space kJ space and increment straight G subscript straight f superscript 0 left parenthesis straight H subscript 2 straight O right parenthesis space equals space minus 228.4 space kJ space mol to the power of negative 1 end exponent

    (i) Processes like solidification of a liquid and liquefaction of a gas are accompanied by a decrease in randomness (entropy). If randomness factor were the only criterion of the spontaneity of a reaction, then these processes would not have been feasible. In other words, the tendency to acquire maximum randomness (entropy) is a factor which determines the spontaneity of a reaction, but it is not the sole criterion.

    (ii) We know that,



    Substituting the values, we have,
       
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    What do you understand by the terms: the system and surroundings?

    A system in thermodynamics refers to that part of the universe in which observations are made and remaining universe constitutes the surrounding. The surroundings include everything other than the system. System and the surroundings together constitute the universe.

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    (i) Define first and the second law of thermodynamics in the combined form. 
    (ii)  
    (a) Write an expression for the entropy change of an ideal gas for isothermal change.
    (b) Write an expression for entropy change for an ideal gas for isobaric change.

    (iii) Calculate the maximum work obtained when 0.75 ml of an ideal gas expands isothermally and reversibly at 27°C from a volume of 15L to 25L.

    (i) The energy of the universe is constant but the entropy of the universe is continuously increasing and tends to a maximum.
    (ii)
    (a)
     


    Substituting the values, we have, 


                

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