Question

what is the eventually change during the process in which 100g of water at 50.0degree Celsius is cooled to ice at -30 degree Celsius

Answer 1

50^oC -----------------> 0^oC ---------------------------> -30^oC

mass = 100 g

moles of water = 100 / 18 = 5.56

here there are three energy conversions

1)   50^oC -----------------> 0^oC

Q1 = m Cp dT

Q1 = 100 x 4.18 x (50-0)

Q1 = 20900 J = 20.9 kJ

2) at 0^oC

Q2 = delta H x moles

       = 6.01 x 5.56

      = 33.4 kJ

3) 0 to -30 oC

Q3 = m Cp dT

Q3 = 100 x 2.09 x 30

Q3 = 6270 J

Q3 = 6.27 kJ

total energy = Q1 + Q2 + Q3

                   = 60.6 kJ

energy chnage in the process = 60.6 kJ energy released