What amount of heat is given off by a glass of boiling water (200g), cooling down to a temperature of 20 degrees?

The amount of heat given off by boiling water during cooling can be calculated using the formula:
Q = C * m * (tc – tn), where Q is the amount of heat given off by boiling water (J), C is the specific heat capacity of water (C = 4200 J / (kg * K)), m is the mass of boiling water (m = 200 g = 0.2 kg), tк is the final water temperature (tк = 20 ºС), tн – the initial water temperature (tн = 100 ºС).
Let’s calculate the amount of heat given off by boiling water:
Q = С * m * (tк – tн) = 4200 * 0.2 * (20 – 100) = -67200 J = -67.2 kJ.
Answer: A glass of boiling water will give 67.2 kJ of heat.