A standard air conditioner involves a refrigerant that is typically now a fluorinated hydrocarbon, such as CH₂F₂. An air-conditioner refrigerant has the property that it readily vaporizes at atmospheric pressure and is easily compressed to its liquid phase under increased pressure. The operation of an air conditioner can be thought of as a closed system made up of the refrigerant going through the two stages shown here (the air circulation is not shown in this diagram).

During expansion, the liquid refrigerant is released into an expansion chamber at low pressure, where it vaporizes. The vapor then undergoes compression at high pressure back to its liquid phase in a compression chamber. (e) Suppose that a house and its exterior are both initially at 31 °C. Some time after the air conditioner is turned on, the house is cooled to 24 °C. Is this process spontaneous or nonspontaneous?

Video transcript

Welcome back everyone. We're told that refrigerant used in air conditioning systems can easily undergo vaporization at atmospheric pressure and compression at higher pressures. The system then acts as a closed system consisting of the refrigerant and undergoing these two stages. The vaporization occurs in an expansion chamber at low pressures. The compression of the vapor back to its liquid phase occurs in a compression chamber at high pressures. So a house and its exterior are initially at 35°C. But after turning on the air conditioner, their houses cooled to 25°C. Is this process non spontaneous or spontaneous. So recall that a spontaneous process requires no input of energy or other in other words, no intervention. So based on our given diagram, we want to recognize that the vaporization A. K. A. Expansion of our liquid becoming a vapor is going to be a spontaneous process. Whereas on the other hand, when we go from our vapor form back to a liquid form here through compression A. K. A condensation, We're going to recognize that this process is non spontaneous. Now going back to our prompt, we're told that we have an initial temperature of 35°C, but then we have the house that is cool too. Now 25°C. And based on our diagram, we want to recognize that spontaneous processes, specifically all spontaneous processes are irreversible, which is why it makes sense as to why we can't go from vapor back to liquid in a spontaneous process. This process is going to be non spontaneous. Now, when our temperature of the house decreases to 25°C, we want to recognize that cooling does not occur without intervention cooling. The house is going to require some intervention through the air conditioner, and the prompt states that we do turn on the air conditioner. And so we do have some intervention occurring, meaning that therefore the process of the Temperature of the house cooling from 35°C to 25°C is going to be a a sorry, non spontaneous process, since it required intervention and our final answer is going to be non spontaneous. So I hope that everything I explained was clear. If you have any questions, please leave them down below and I'll see everyone in the next practice video.