Assume that the surrounding atmospheric pressure stays constant and the air contained in a room (treated as an ideal gas) maintains this pressure by communicating with the surroundings through windows, doors, etc. As the temperature changes between day and night, the internal energy of the air in the room:

Step-by-step solution

The internal energy of an ideal gas is given by U = f 2 n R T , where f is the degree of freedom, n is the number of moles, R is the universal gas constant, and T is the absolute temperature. From the ideal gas equation, P V = n R T . Substituting this into the expression for internal energy, we get U = f 2 P V . Since the room communicates with the surroundings, the pressure P of the air inside the room remains constant and equal to the atmospheric pressure. The volume V of the room is also constant. Because both