Warm up: write this question and answer in your spiral As a substance such as water is cooled down, the atoms and molecules undergo a– a. physical change as they move faster b. physical change as they move slower c. chemical change as they move faster d. chemical change as they move slower

The Heating/Cooling Curve of Water

Objective I will determine at what temperature a substance will freeze, melt, boil or condense by looking at a heating curve. With a given set of data, I will prepare a graph showing the heating curve of water. I will know that I have mastered this when I can identify phase changes for any substance and determine whether energy is absorbed or released during each change.

Discussion Procedure: Place 4-5 ice cubes (less than 100 g) in a 250 ml beaker. Using the thermometer, determine the starting temperature and record it in a data table like the following: (make it larger, you will need several minutes at 30 second intervals) Time in seconds Temperature in Celsius TimeTemp 0 sec.2:00 :302:30 1:303:00

Discussion Place the beaker with the ice and thermometer on a hot plate. Turn on the hot plate and begin stirring with the stir stick that is provided. Do not use the thermometer to stir. Stirring will prevent hot and cold spots.

Discussion Stir continuously recording the temperature every 30 seconds until the water is boiling and the temperature does not change over a 3 minute period. One person should keep time, one should take temperature readings and everyone should record.

Lab Results: Completed and attached into composition book Identify the independent and dependent variables, then make a graph using 30 second intervals for time. Your graph must include the following: Title (The Heating Curve of Water) X (time in minutes) and Y (temp in o C) axis labeled An appropriate scale numbered Data plotted and line drawn

Data to be Graphed Time SecondsTemp CelsiusTimeTemp Celsius :0 0-25:3045 :306:0055 1:0006:3065 1:3007:0075 2:0007:3080 2:3028:0085 3:0068:3090 3:30109:0095 4:00159: :302510: :003510:30100

Conclusion Questions: answered in composition book 1. What is the independent variable in your investigation? 2. What is the dependent variable in your investigation? 3. What is the basic shape of your graph? 4. Based on this shape, how does the temperature of the ice change as it is continually heated?

5. Label the three sections of your graph with A, B, and C. 6. What do you think is happening in Section A of the graph? 7. What do you think is happening in Section B of the graph? 8. What do you think is happening in Section C of the graph?

9. Why do you think the temperature remains constant during melting even though we continued to heat? 10. Why do you think the temperature is constant during boiling even though we continued to heat? 11. Define melting, freezing, boiling, and evaporation.

12. What is the melting temperature of ice? 13. What is the freezing temperature of water? 14. Compare and contrast melting and freezing. 15. Compare and contrast evaporation and boiling.

Heat is entering Endothermic Heat is leaving Exothermic Melting Freezing Vaporizing Condensing Boiling

Heating Curve (used to identify Phase Changes)

This diagram shows the melting and boiling points for a crystalline substance. Temperature is on the y- axis & either the amount of energy absorbed or released or the time is graphed on the x-axis.

Between the temperatures represented by points A and B, the substance will exist in a solid state. As heat is added the particles will vibrate faster & thus have an increase in kinetic energy & an increase in temperature.

The temp represented by B is the melting point of the substance. The flat line indicates that heat is being added (absorbed), but the temp is not increasing, thus there is no change in KE between points B and C. At time B, the substance is all solid. At time C, the substance will be all liquid. The energy needed to change the substance from a solid to a liquid is called “heat of fusion”. What is the melting point of this substance?

At Point C, the KE begins increasing and continues to increase until the substance reaches its boiling point, represented by point D. Since temperature is directly related to KE, the temperature is also increasing during segment CD.

At point D, the liquid begins to boil and changes into the gaseous state. The energy needed to change the liquid to a gas is called “Heat of vaporization”. During segment DE the substance is both liquid and gas. At point E, all of the liquid has become a gas and the KE begins increasing as indicated by the positive slope of the line. An increase in KE means an increase in temperature and an increase in speed of particles. What is the boiling point of this substance?

Solid Liquid Temp and KE Increasing Gas Solid and Liquid Melting Freezing Liquid and Gas vaporization Condensation No Change in KE or Temp

Crystallization and solidification can be considered synonyms for freezing. For crystalline substances, melting point and freezing point will be the same temperature and boiling point and condensation point will be the same temperature. Sublimation is the process of changing from a solid to a gas without going through the liquid state