Question

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

Answer 1

Energy releases to the surroundings = -32.2 kJ

Further explanation  

Heat can be calculated using the formula:  

Q = mc∆T  

Q = heat, J  

m = mass, g  

c = specific heat, joules / g ° C  

∆T = temperature difference, ° C / K  

mass of coffee(m) = 140 g

∆T = temperature difference :

final temperature - initial temperature = 20-75=-55°C

specific heat coffee= specific heat water = 4.18 J/g° C  

The heat releases :

$\tt Q=140\times 4.18\times -55\\\\Q=-32186~J\approx -32.2~kJ$