Name: ______

Melting and Freezing Directions: Read, highlight, and once you are finished reading, go to schoology.com and answer the questions. Melting When solids turn to liquids, we call this change of state melting. The temperature where a substance turns from a solid to a liquid is called the melting point. Every substance on earth has a different melting point. Water, for example, has a melting point of 32oF (0oC). When melting occurs, the molecules are absorbing heat. Here’s the weird part though, they don’t vibrate faster. You saw this in the lab when you thought your thermometer was broken. The heat goes into break the attraction that the molecules have to each other. When they are strong enough to break away, they can move from their fixed position becoming a liquid. Then they can vibrate faster. Because molecules that are melting are absorbing heat, we refer to melting as an endothermic process. Endo means “to enter” while thermic means “heat.” Freezing The reverse of melting (liquid back to solid) is called freezing. The temperature where freezing occurs is exactly the same as the melting point. Water, for example, has a freezing point of 32oF (0oC). The one big difference is that while melting occurs when heat energy is added, freezing occurs when heat energy is taken away. For freezing, the molecules are changing from being faster to being slower. When freezing occurs, the molecules are giving off heat. Here’s the weird part though, they don’t vibrate slower while they are freezing (have you heard this before?). As the heat is given off, the molecules become more and more attracted to each other. When they are no longer strong enough to avoid being attracted to each other, they “freeze” in place. Remember, even though they are “frozen” in place, they still vibrate back and forth ever so slightly. Because the molecules are giving up their heat (getting colder), we refer to freezing as an exothermic process. Exo means “to exit” while thermic means “heat.”

Complete the following chart for Water in degrees Celsius Melting Freezing Temperature where it occurs? Endothermic or Exothermic change? Temperature climbing or staying the same?

Remember to go to schoology.com and answer the questions.