The freezing point of a solution is
A. lower than the freezing point of the solvent alone because higher temperature is required to accelerate solvent molecular motion enough to overcome obstructon by solute particles..
B. lower than the freezing point of the solvent alone because lower temperature is required to accelerate solvent molecular motion enough to overcome obstruction by solute particles.
C. higher than the freezing point of the solvent alone because higher temperature is required to accelerate solvent molecular motion enough to overcome obstruction by solute particles.
D. lower than the freezing point of the solvent alone because lower temperature is required to slow solvent molecular motion enough to overcome obstruction by solute particles.
E. None of these are true.
http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/meltpt.html
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http://en.wikipedia.org/wiki/Freezing-point_depression
The freezing point of a solution is a property that differs from the freezing point of the solvent alone. To understand why this is the case, we need to consider the effect of the solute particles on the freezing process.
When a solute is added to a solvent, it disrupts the regularity of the solvent's crystal lattice structure during freezing. This interference is caused by the solute particles occupying spaces between the solvent molecules. As a result, a higher temperature or lower temperature is required for the solvent to overcome this obstruction and freeze.
Option A states that the freezing point of the solution is lower than the freezing point of the solvent alone because a higher temperature is required to accelerate solvent molecular motion enough to overcome obstruction by solute particles. This is incorrect because it suggests that the solution has a higher freezing point, which is not true.
Option B states that the freezing point of the solution is lower than the freezing point of the solvent alone because a lower temperature is required to accelerate solvent molecular motion enough to overcome obstruction by solute particles. This is the correct answer. By adding a solute, the solution's freezing point is lowered, and the solvent needs a lower temperature to solidify.
Option C states that the freezing point of the solution is higher than the freezing point of the solvent alone because a higher temperature is required to accelerate solvent molecular motion enough to overcome obstruction by solute particles. This is incorrect because it suggests that the solution has a higher freezing point, which is not true.
Option D states that the freezing point of the solution is lower than the freezing point of the solvent alone because a lower temperature is required to slow solvent molecular motion enough to overcome obstruction by solute particles. This is incorrect because it confuses the effect of temperature on solvent motion with the freezing point of the solution.
Therefore, the correct answer is B. The freezing point of a solution is lower than the freezing point of the solvent alone because a lower temperature is required to accelerate solvent molecular motion enough to overcome obstruction by solute particles.