Question

How much heat will be released by the system when 1.0 L of hot water, initially at 80 oC, cools down to 20 oC? (c = 4.18 J/K g)

A) 250 kJ

B) 250 J

C) None. Heat will instead be absorbed

D) More info is needed to answer

Answer 1

Amount of heat released, Q = mcdt

Where

m = mass of hot water = Volume x density

                                  = 1.0 L x ( 1kg/L)

                                  = 1.0 kg

                                  = 1000 g

c = specific heat of water = 4.18 J/(K-g)

dt = change in temperature = (80+273) - (20+273) K

                                        = 60 K

Plug the values we get Q = 1000.0 x4.18x60 J

                                     = 250800 J

                                     = 250 kJ

Therefore option (A) is correct.