Question

Example An ideal gas undergoes the cyclic process abca (see Fig). During the transitions a → b → c it absorbs a net heat of 4.5 k.J. The thermal energy at point a is 600 .J The nature of the transtonc a is unknown. 3o E

Answer 1

from first law of thermodynamics heat supplied to system utilised to increase the thermal energy and also to do work.

Given thermal or internal energy at a V_a = 600 J Q_ab + Q_bc = 4.5 kJ and Q_net = 1 from first law of Thermodynamics dQ = dv + dw implies Q_abc = dv + w_ab (Q_ab + Q_bc) = (v_c - v_a) + (w_ab + w_bc) 4.5 times 10^3 = (v_c - 600) + [0 + p(v_c - v_b)] u_c = 4500 + 600 -100 times 10^3[6 - 2] times 10^-2 u_c = 1100 J Thermal energy at C c) In cyclic process dv = 0: dQ = dw Net heat absorbed dQ = Q_ab + Q_bc + Q_ca 1 times 10^3 = 4.5 times 10^3 + Q_ca Q_ca = -3500 J Q_ca = -3.5 KJ (Heat is released by system) b) dQ = W_ab + W_bc + W_ca w_ca = 10^3 - (w_ab + w_bc] = 100 - 4000 = -3000 J from first law of thermodynamics heat supplied to system utilized to increase the thermal energy and also to do work

Heat supplied and work done are path dependent and thermal energy depends on state that's why for complete cycle Cheng's in thermal energy is zero