Question

A volume of 60.0 liters of liquid ethanol at 70.0°C and 65.0 L of liquid water at 20.0°C are to be mixed in a well-insulated flask. The energy balance for this constant pressure process is Q = ΔH. Neglecting evaporation and the heat of mixing, estimate the final mixture temperature.

Answer 1

mass of liquid ethanol = 60 x 10^3 x 0.789

                                 = 47340 g

heat capacity of ethanol = 2.46 J/g oC

mass of water = 65 x 10^3 x 1 = 65000 g

heat capacity = 4.18 J/g oC

here heat loss by liquid ethanol = heat gain by liquid water

47340 x 2.46 x (70 - Tf) = 65000 x 4.18 x (Tf - 20)

Tf = 35 oC

final mixture temperature = 35 oC