1. Chapter 14 – Liquids and Solids 14.1 Water and Its Phase Changes Pgs 492 - 497

2. Water’s Unique Properties Water is LESS dense as a solid than a liquid! –Why ice floats on a lake Water has a high surface tension –Hydrogen bonding forms a protective “skin” on the top of water Water has a HIGH boiling and melting point

3. Water and Its Phase Changes What happens when we heat liquid water – think KMT people!!! –The motions of the water molecules increase as its heated Disrupts H-bonds between water molecules Bubbles start to form What happens when we reach 100 o C? –Reach the BOILING POINT The bubbles float to the surface and burst! The temperature will NOT CHANGE until all of the water has been turned into vapor –Once all of the water has been converted into vapor, then the temperature will rise (we are heating the vapor)

4. Water and It’s Phase Changes What happens when we cool water? –The temperature of the water will decrease until it reaches 0 o C What happens here??? –Reach the FREEZING POINT ! –The temperature will remain at 0 o C until all of the liquid water has changed to ice The temperature will then drop as cooling continues (of the ice)

5. Heating/Cooling Curve of Water

6. Amount of Heat Need Between Phase Changes (when you heat a substance ) Use the Specific Heat equation from 1 st semester!!! –Allows us to determine how much heat we need to reach the next phase change!!

7. Examples! How much heat is needed to heat a pot of water from 16 o C to 52 o C if the water has a mass of 112g? How much heat is lost or required when 8.2g water vapor is cooled from 112 ˚C to 102˚C

8. Energy Requirements for the Changes of State Changing state from solids to liquid to gas requires energy – why? –You must OVERCOME the intermolecular forces!! The energy required to melt 1 mol of a substance is called the molar heat of fusion –For ice = 6.02 kJ/mol The energy required to change 1 mol of a liquid to its vapor is called the molar heat of vaporization –For water = 40.6 kJ/mol at 100 o C

9. Energy Requirements for the Changes of State The plateau seen with the vaporization of water is MUCH longer than the plateau seen with melting ice. Why?

10. Calculating Energy Changes How much heat is required to completely melt 23.5g of ice at 0 o C? How much heat must be removed or added to completely condense 243.1g of water vapor at 100 o C?

11. Calculating Energy Changes: Liquid to Gas How much heat is required to make 32g of water at 23 o C into water vapor at 100. o C?

12. Now you try one! How much heat is required or released to make 62g of water at 23 o C ice at -12 o C?