Is thermal energy added in freezing and what happens to a substance when thermal energy is added?
Murtadha Shukur
No, thermal energy is not added when a substance freezes. In fact, the opposite happens! Freezing is a phase change from a liquid to a solid, and during this process, thermal energy is released from the substance. This released energy is called the latent heat of freezing.
Here's why:
- In a liquid, the molecules are relatively free to move around. Adding thermal energy to a liquid increases the average kinetic energy of its molecules, making them move faster and causing the temperature to rise.
- During freezing, the molecules lose kinetic energy and become more ordered, forming a regular crystal lattice structure. This ordering process requires energy to overcome the forces holding the molecules apart in the liquid state.
- The energy released by the molecules as they lose kinetic energy and become more ordered is the latent heat of freezing. This energy does not cause the temperature to change because it is used to break the intermolecular bonds in the liquid, not to increase the kinetic energy of the molecules.
So, when you add thermal energy to a substance, it generally increases in temperature. But when a substance freezes, it releases thermal energy and does not change temperature until all the liquid has frozen.
Here are some additional points to remember:
- The amount of latent heat released during freezing is specific to each substance. For example, water releases about 334 kJ/kg of latent heat when it freezes.
- The latent heat of freezing can be used to explain why ice can sometimes feel colder than air at the same temperature. When ice comes into contact with your skin, it draws heat away from your body to melt, making your skin feel cold even though the air temperature is not that low.
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