Why does an impurity reduce the melting point of a substance?

Answer 1

if impurities are present in water, it will freeze at a temperature less than 0.c

this is due to the factor in the melting point depression equation, but this equation only holds for pure liquids and "impure" liquids, commonly refered to as "solutions".

It's a different story for solids, however. I guess the basic answer to your question would be that impurities affect the crystal structure of a solid. Incindentally this leads to lowering and widening of the interval of temperature in which either of the two (or more) pure solid components would melt.

I'm assuming that since your question refers to solids and not liquids or aqueous solutions, your are in your first semester of Organic Chemistry? Good luck to you.

Answer 2

Impure substances have different melting/ freezing points than their pure counterparts because the substance that was dissolved into the pure substance had a different melting point (higher or lower depending on the substance). When the freezing points of the two substances average out, a new freezing point is created. The freezing point/ melting is not necessarily lower

Answer 3

Impurities decrease vapor pressure, which decreases melting point (and increases boiling point.) One way to think of it is that impurities get in the way of the bonds that would be holding the solid together. By disrupting the normal organization of atoms or molecules in that solid, the impurities weaken the bonds holding the solid together (keep in mind these are bonds BETWEEN atoms and molecules, not within them).

As these intermolecular bonds weaken, it takes less energy to pull the molecules apart, which means it will melt to a liquid at a lower temperature.

Answer 4

Because a solution with impurities has a lower volatility. The mole fraction of the solvent is also decreased.

Answer 5

give answer the above the quation

Answer 6

Impurities disrupt the regular arrangement of particles and hence, the bonding. And so less energy is needed to break the bonds so MP decreases.

In liquid state, particles are moving and would rearrange themselves to achieve maximum attraction, and hence stability. Thus more energy is needed to break the bonds and BP increases.