Understand Freezing point/Melting point

I decide to create this blog to document things that could have been simplified even more for understanding. I have stumbled upon many things that could be explained in a different way. This blog will be mostly about science.

My first topic is about freezing/melting point. What does it even mean when people say adding salt lowers the freezing point? Do you actually know what that means?

Freezing point is defined as the TEMPERATURE that liquid begins to freeze into solid.

Here is the equation from Wikipedia:

ΔT_F = K_F · b · i

• ΔT_F, the freezing point depression, is defined as T_{F (pure solvent)} - T_{F (solution)}.
• K_F, the cryoscopic constant, which is dependent on the properties of the solvent, not the solute. Note: When conducting experiments, a higher K_F value makes it easier to observe larger drops in the freezing point. For water, K_F = 1.853 C°·kg/mol.^[5]
• b is the molality (mol solute per kg of solvent)
• i is the van 't Hoff factor (number of ion particles per individual molecule of solute, e.g. i = 2 for NaCl, 3 for BaCl₂)

Many people use salt to lower the freezing point of the ice. What does it mean? Imagine the temperature for today is 0 C. This is also the temperature when ice forms. Adding salt to the ice will lower it to -6 C. This means liquid will be frozen into solid at now -6 C (used to be 0 C). Since today's temperature is 0 C, the ice on the road after addition of salt is going to melt because we haven't reached -6 C (the new freezing point) yet. Until then, everything will be stayed at liquid.

We also can understand it in terms of melting point. By the way, freezing point is pretty much the same as melting point (by definition). Melting point is just the temperature when solid melts into liquid. If you lower the melting point, that could be interpreted as it takes less heat to melt the ice. For example, say it today's temperature is 15 C. It takes 20 C to melt the ice, but now after adding the salt, the new melting point is 15 C. You are now melting the ice, changing it into the liquid form.

This is mainly for personal use. I do not hold any responsibility for any inaccurate information.