Answer to Question #166962 in Molecular Physics | Thermodynamics for Mercy

Question

A beaker of hot water is placed on the bench. Describe all the ways in which it looses heat and suggest a simple way of minimizing each.

Answer 1

A beaker of hot water can lose heat via conduction, convection, thermal radiation, and evaporation. Let's look at each one individually.

Thermal radiation is the loss of heat from a solid object into the atmosphere via the release of electromagnetic radiation. So the hot outer edge of the beaker will lose its heat to the surrounding air via thermal radiation. Cover the outer edge of the beaker with some heat insulating fabric.

Conduction is the movement of heat along a gradient within a solid. So the inner part of the beaker against the hot liquid will transfer that heat to the cooler outer part of the teacup (where it will be lost via thermal radiation, so covering of the edge will prevent this too).

Convection is the movement of molecules of a liquid or gas within itself. So hot molecules of water in the middle of the beaker will eventually make their way to the outer part of the water near the beaker where they will lose their heat. Don't stir the content of a beaker and cover it with a lid.

Finally, evaporation is the conversion of liquid water to gaseous water. Since gaseous water is in a higher energy state than liquid water, energy is required for the water to evaporate. The energy in this case comes from the heat of the water. As energy is lost due to evapration, the water slowly cools as a result. This is the reason that a container of a highly volatile liquid always feels cool to the touch since it absorbs the heat from your fingers to evaporate the liquid. Cover the beacer with a lid to prevent it.