# Why does the freezing point of a sample gas occur at a certain temperature? [closed]

From "North Carolina Measures of Student Learning: NC’s Common Exams Chemistry" (Source, Number 20):

The graph below shows a cooling curve for a sample of gas that is uniformly cooled from $155~^\circ\mathrm{C}$.

Why does the freezing point of the substance occur at $–20^\circ\mathrm{C}$?

1. because the latent heat energy is absorbed by the substance as it is converted from a liquid to a solid
2. because the latent heat energy is released into the air as the substance is converted from a liquid to a solid
3. because the average kinetic energy is increasing for the substance as it is converted from a solid to a liquid
4. because the average kinetic energy is decreasing for the substance as it is converted from a solid to a liquid

Its really just a simple questioning and I think the answer is 3, because the average kinetic energy is increases when converted from solid to liquid. Any reason why I'm wrong and the answer says it is 2?

• Could you move the question from the file into the above? Also, please provide a more descriptive title. – jerepierre Jan 10 '15 at 0:43
• @AwesomeFlame123 As you can see, it was neither a problem to move the question into the posting nor was it difficult to give it a more descriptive title. Please invest some more time in asking your questions, people replying here do that on their own free time and they deserve some appreciation for that they are helping you. Not even trying to type the question into the post, I would consider rather rude. – Martin - マーチン Jan 13 '15 at 5:06