Question

A cup of coffee (140g) cools from 75°C down to comfortable room temperature 20°C. How much energy does it release to the surroundings

Answer 1

Given that the mass of coffee in the cup = 140 g

Final temperature = $20^{0}C$

Initial temperature = $75^{0}C$

Let us assume the specific heat of coffee is equal to that of water = 4.184$\frac{J}{g^{0}C }$

Temperature change = T(final) - T(initial) = (20 - 75 )$^{0}C$

                                                                   =- 55 $^{0}C$

-Heat given out by coffee = heat absorbed by the surroundings

Heat released into the surroundings =-($mC(T_{final}-T_{initial})$)

                                             = $-(140g)4.184\frac{J}{g^{0}C }( -55^{0}C)$

                                             = 32,217 J