Question

In a water-cooled engine, running under constant conditions, 11.7 kJ of heat energy is transferred from the engine to the water coolant every second. If the water is flowing at a rate of 13.1 L/min, in a closed circuit between the engine and the radiator, by what amount must the temperature of the water be reduced by the radiator before it returns to the engine? Assume that the density of water is 1.00 g/cm3 and the molar heat capacity of water is 75.4 J/mol/K. (Give your answer to the nearest 1 degC or 1 K.)

Answer 1

flow rate of water= 13.1 L/min, density of water = 1g/cc. = 1000g/L ( 1000cc= 1L)

flow rate of water in g/min= 13.1 L/min* 1000g/L= 1.31*10⁴ g/min

molar flow rate of water =mass flow rate of water/ molar mass = 1.31*10⁴/18 = 728 moles/min

=728/60 moles/min = 12.13 moles/sec

heat removed by water =molar flow rate of water* specific heat* temperature difference = 11.7*1000 J/sec

12.13*75.4*drop in temperature = 11.7*1000

drop in temperature = 11.7*1000/(12.13*75.4)= 12.79 deg.c