# Thermodynamics and microwaving food

• berra
In summary, the conversation discusses the observation of a plastic container buckling after being microwaved and the thermodynamic variables that could have caused this. The discussion also raises questions about the use of different containers and ensembles for thermodynamic computations. It is suggested to use a different type of dish for microwaving food and to avoid using plastic containers due to potential warping and chemical contamination.
berra
Hi, I just microwaved some food in a plastic container and noticed that it started to buckle inwards. So I wonder what thermodynamic variables were constant? Obviously not the volume V. The number of particles N was probably approximately constant. What more than N was constant?? What ensemble should I use if I want to do computations on this??

What computations? Use a different type of dish to microwave your food.

Thermodynamical computations. Gibbs free energy requires temperature and pressure constant, for example. But the temperature is certainly not constant when heating in a microwave.

berra said:
Hi, I just microwaved some food in a plastic container and noticed that it started to buckle inwards. So I wonder what thermodynamic variables were constant? Obviously not the volume V. The number of particles N was probably approximately constant. What more than N was constant?? What ensemble should I use if I want to do computations on this??
If it buckled inwards (and warpage of the plastic was not a problem, see SteamKing response), some mass of water vapor must have escaped from the container during the heating. If it only buckled when the container cooled down, then this is almost certainly what happened. When the container cooled, the remaining water vapor in the container mostly condensed, and this created a partial vacuum in the container. The walls were not structurally stiff enough to support the pressure difference.

Chet

Alternatively the plastic container warped with the heat and became permanently warped. If that's the case then
1st: The volume changed because the container changed, particles were most likely lost. N is not conserved.
2nd: The plastic outgassed some chemicals into your food contaminating it. I wouldn't use this kind of container in the micro-wave any more.

## 1. How does a microwave heat up food?

Microwaves use a form of electromagnetic radiation to heat up food. This radiation is absorbed by the water, fat, and sugar molecules in the food, causing them to vibrate and generate heat.

## 2. Does microwaving food change its nutritional value?

Microwaving food does not significantly change its nutritional value. However, like any cooking method, some nutrients may be lost due to heat exposure. It is important to use proper cooking techniques and not overcook food in the microwave.

## 3. Can microwaving food cause it to become radioactive?

No, microwaves do not make food radioactive. Microwaves use non-ionizing radiation, which does not have enough energy to change the molecular structure of food or make it radioactive.

## 4. Is it safe to microwave food in plastic containers?

Some plastic containers may release chemicals into food when heated, so it is important to use microwave-safe containers. Look for containers labeled "microwave-safe" or use glass or ceramic containers instead.

## 5. Why does food sometimes heat unevenly in the microwave?

The shape and size of the food, as well as the placement in the microwave, can affect how evenly it heats up. Microwaves work by heating up the water molecules in food, so if there are areas with higher or lower water content, those areas may heat up differently.

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