What do you understand by:(i) Isothermal process(ii) Adiabatic p
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    What do you understand by:
    (i) Isothermal process
    (ii) Adiabatic process
    (iii) Isobaric process
    (iv) Isochoric process
    (v) Cyclic process?

    (i) Isothermal process: A process is said to be isothermal if the temperature of the system remains constant i.e. operation is carried at a constant temperature. For an isothermal process, dT = 0 where dT is the change in temperature.

    (ii) Adiabatic process: In an adiabatic process, no heat can flow from the system to the surrounding or vice versa i.e. the system is completely insulated from the surroundings.

    (iii) Isobaric process: It is the process during which the pressure of the system is kept constant i.e. dP = 0. The volume may or may not change.

    (iv) Isochoric process: It is a process during which the volume of the system is kept constant i.e dV = 0.

    (v) Cyclic process. When a system undergoes a series of changes and finally returns to its initial state, it is an example of the cyclic process. In cyclic process dU = 0.

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    Derive an expression for pressure-volume work (PV – work).
    Let us consider a gas enclosed in a cylinder fitted with a frictionless piston having an area of cross-section equal to ‘a’. Let the gas expand against the external pressure P facing the piston to move through a small distance d. Then work of expansion is given by,



           

    During expansion, work is done by the system and ∆V(V2 – V1) is positive. Therefore, in order to satisfy the sign conventions, a negative sign is put in the expression for work.



    During compression, Work is done on the system. ∆V(V2 – V1) for compression is negative. Therefore work, as obtained from the above expression, comes out to be positive and satisfies the conventions.
    The general expression for all types of PV-work is given by
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    Answer

    Derive an expression for work done in isothermal reversible expansion of ideal gas.

    Let us consider n moles of ideal gas enclosed in a cylinder fitted with a weightless and frictionless piston. The work of expansion for a small change of volume dV against the external pressure P is given by
                              
     Total work done when the gas expands from initial volume V1 to final volume V2, will be

                     
    For an ideal gas, PV = nRT i.e.

                       
    Hence,
         
     

    For isothermal expansion, T = constant so that

        

    But at constant temperature,

                            P1V1 = P2V2
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    Answer

    What do you mean by internal energy and internal energy change?

    The total energy stored by a fixed amount of the substance is called its internal energy or intrinsic energy and is denoted by U. It is the sum of various forms of energies such as kinetic energy of translation, rotation and vibration, potential energy due to intermolecular forces, the chemical bond energy and electronic and nuclear energies of the constituent atoms.


    Internal energy is a function of state only. It is not possible to determine the absolute value of internal energy as most of the constituent energies cannot be precisely determined. However, we are more interested in knowing the change in internal energy (∆U).

    Change in internal energy (∆U): It may be defined as The difference in internal energies of the product and reactant species taking part in a chemical reaction at constant volume. For example, if UR represents the internal energy of the reactants and Up represents the internal energy of the products, then

    where ∆U gives the change in internal energy.

    In a chemical reaction, ∆U has always noticed in the form of heat evolved or absorbed during the reaction in case the reaction is carried out at constant volume. Hence internal energy change (∆U) is equal to the heat evolved or absorbed in a chemical reaction at constant volume and constant temperature.

     
    Clearly, if  the extra energy possessed by the system in the initial state (or the reactants) would be given out and  will be negative. 

    Similarly, if  energy will be absorbed in the process and  will be positive.
    Units of U: The units of energy are ergs (in CGS units) or joules (in S.I. units)
    1 Joule = 107 ergs. 
       
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    Answer

    Give the points of difference between reversible process and irreversible process.

    Reversible process

    Irreversible process

    1. Such processes take place infinitesimally slowly and their direction at any point can be reversed.

    1. The process cannot be reversed.

    2. It is a slow process.

    2. It is a fast process.

    3. This process is in equilibrium at all stages of operation.

    3. There is no equilibrium.

    4. This is an ideal and imaginary process.

    4. It is a real process.
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