Question

If a refrigerator/freezer gets cold through its expulsion of heat, why is it that when I took out a frozen ice cream bar and held it in a warm room, I felt cold air from it? I thought coldness was the absence of heat, like in outer space or winter.

Answer 1

The phenomenon you experienced with the frozen ice cream bar is related to how heat moves and the transfer of energy. It might seem counterintuitive, but I'll explain why it happens.

First, let's understand how a refrigerator/freezer works:

Refrigerators and freezers operate using a cooling cycle that involves a refrigerant (usually a gas or liquid) being compressed, then expanding. This process allows the refrigerant to absorb heat from the inside of the appliance (making it cold) and then expel that heat to the surrounding environment. The expelled heat is usually released at the back or bottom of the refrigerator, away from the interior compartment.

Now, let's consider what happens when you take a frozen ice cream bar from the freezer and hold it in a warm room:

1. Heat Transfer: Heat naturally flows from areas of higher temperature to areas of lower temperature. When you take the frozen ice cream bar (which is very cold) into a warmer room, heat from the room starts transferring to the ice cream bar.

2. Melting: As the ice cream bar absorbs heat, the temperature of the outer layer rises, causing the ice on the surface to melt and convert into water. This process requires heat energy, and it's why the ice cream bar feels cold to your touch. The heat energy from the warm room is being used to melt the ice cream bar instead of raising its overall temperature.

3. Evaporation: Additionally, the melted water on the surface of the ice cream bar may evaporate, taking away more heat energy from the surface and making it feel even colder.

So, when you hold the frozen ice cream bar in a warm room, you're not experiencing the "coldness" as an absence of heat; rather, you're feeling the heat transfer process in action. The heat from the warmer room is being used to melt the ice and evaporate the water on the surface of the ice cream bar, making it feel cold to the touch.

It's important to note that while the ice cream bar is absorbing heat from the room, the refrigerator/freezer is still working to maintain its internal temperature. It's just that the heat being transferred to the ice cream bar outweighs the heat being expelled by the refrigerator at that moment. Eventually, the ice cream bar will reach a balance with the room temperature, and the melting and cooling process will slow down.