Question

4.0 kg of water at 39 degree C is mixed with 4.0 kg of water at 52 degree C in a well-insulated container. Part A Estimate the net change in entropy of the system. Express your answer to two significant figures and include the appropriate units. Delta S = _______

Answer 1

Heat capacity = Cp = 4184 J/kg.K

The change in entropy is given by:

$\Delta S = C_pln{\frac{T_f}{T_i}}$

and the final temperature can be calculated from the following formula:

$T_f = \frac{m_1T_1+m_2T_2}{m_1+m_2}$

T_1 = 273+39 = 312 K

T_2 = 273+52 = 325 K

Tf = (T_1+T_2)/2 = 318.5 K = 45.5 deg C

Hence net change in entropy = 4184*(ln(318.5/312)+ln(318.5/325)) =1.743 J/kg.K