Thermodynamics

Internal energy : (U) U = PE + KE of molecules. Work done by a gas for expansion from volume v1 to volume v2 against a constant external pressure - w = Pext (v2 - v1) = Pext v. Heat absorbed or evolved,  Q, = m.s t where m = mass, s = specific heat,  t = temperature difference Total energy of matter E = Etranslational + Erotational + Evibrational + Ebonding + Eelectronic + ……. According to first law of thermodynamics - E = q + w Enthalpy change, H = E +  (Pv) or H = E +  (nRT). Specific heats of gas C =  Heat capacity C = where q is the heat absorbed to raise the temperature from T1 to T2. Mayer formula Cp - Cv = R Where Cp =  Isothermal Process:  du = 0  dQ = dW = pdV  work done is isothermal reversible expansion wmax = - 2.303 nRT log  Adiabatic process : du + dW = 0  du = - dW  for reversible adiabatic expansion - Pvy = constant Tvy-1 = constant Pv(1 - y)/y =constant Work done during adiabatic expansion of n moles of an ideal gas = nCr (T2 - T1). Kirchoff's equation -  Efficiency of heat engine, =  % efficiency =  For reversible process (equilibrium) = ssystem + ssurr = 0 For irreversible process (spontaneous process) = ssystem + ssurr > 0. Carnot's reversible cycle efficiency  % Efficiency of engine =  In refrigerator, an amount of heat Q2 is removed from sink at lower rejected at higher temperature T1 to the source. Thus, Q2 + W = Q1 or W = Q1 - Q2. Coefficient of performance  = or  Charge in entropy dS = or dS =