A 200g mug of hot tea is at 85∘C when it is placed on a table in a 22∘C room. Assume the specific heat capacity of the tea is the same as that of water, c=4.18J(g∘C), and that the tea eventually reaches the room temperature without losing mass. Any energy exchange other than between the tea and the surrounding air may be neglected.
(a) Calculate the magnitude of the thermal energy transferred between the tea and the surrounding air during the cooling process.
(b) Using the sign convention that Q>0 corresponds to energy entering the system, determine the sign of Q for the tea when the tea alone is defined as the system. Explain whether the tea undergoes heating or cooling.
(c) Now define the system to be the combination of the tea and the surrounding room air. Determine the net thermal energy transfer Q for this combined system and state whether the process is heating, cooling, or neither. Justify your conclusion.
(d) Briefly explain how your answers to parts (b) and (c) illustrate the importance of clearly specifying system boundaries when classifying a process as heating or cooling.