Thermodynamic Process

Card # 28 Thermodynamic

Process

A thermodynamic process involves change of heat energy into mechanical energy by changing thermodynamic variables like P, V, T or internal energy etc with time.

Isothermal Process It is a thermodynamic process in which the temperature remains constant. We know the ideal gas equation for 1 mole of gas is PV = RT Since T = constant, PV= constant or P1 V 1 = P 2 V 2 The internal energy of an ideal gas depends only on temperature. Since temperature is constant (ΔU = 0). Hence for Isothermal process 1st law of thermodynamics Q=W=PΔV

⎛V ⎞ W = 2.303log10 ⎜ 2 ⎟ ⎝ V1 ⎠ For Isothermal expansion V2 > V1 work done (W) will be positive. For Isothermal compression V2 < V1 work done (W) will be negative.

Adiabatic Process It is a thermodynamic process in which amount of heat energy is kept constant i.e., heat is neither allowed to enter or leave a system. Application of 1st law to adiabatic process Q = ΔU + W (From first Law) and since Q=0 Therefore ΔU = -W = -PΔV Ideal gas equation for adiabatic process is PV y = cons tan t Where y =

Cp Cv

= ratio of specific heats

Thus for change in State from ( P1 , V 1 ) to ( P 2 , V

P1 V 1 y = P 2 V

2

)

y 2

and work done in case of adiabatic process is W = R ( T1 – T2) γ-1 Here T1 = initial temperature & T2 = final temperature of the system.

Isobaric Process It is a thermodynamic process in which pressure is kept constant. Work done in case of Isobaric Process is W = P ( V 2 − V 1 ) Here V2 = Final volume of the gas & V1 = Initial volume of the gas.

Isochoric Process It is a thermodynamic process in which pressure is kept constant. Work done in case of Isochoric process is W = 0 Since dV = 0 = no change in volume of gas.

Quasi-Static Process It is the process in which the system changes its variables (P, V, T) so slowly that it remains in thermal and mechanical equilibrium with its surroundings throughout the

process. It means Quasi-Static process is infinitely slow process. At every stage the difference in the pressure and temperature of the system and its surrounding remains infinitesimal.