If your air conditioner is more than several years old, it may use the chlorofluorocarbon CCl₂F₂ as the heat transfer fluid. The normal boiling point of CCl₂F₂ is −29.8°C, and the enthalpy of vaporization is 20.11 kJ/mol. The gas and the liquid have molar heat capacities of 117.2 J/mol ∙ K and 72.3 J/mol ∙ K, respectively. How much energy is evolved as heat when 20.0 g of CCl₂F₂ is cooled from +40°C to −40°C?