An Experiment to Determine the Heating and Cooling Curves of Water
NS 10.5
(pg 1 of 2)
Heating and Cooling Curves
What happens when we heat a sample of ice that is initially at -15°C? The addition of heat causes the temperature of the ice to increase. As long as the temperature is below 0°C, the sample remains frozen. When the temperature reaches 0°C (the melting point of water), the ice begins to melt. Because melting is an endothermic process, the heat we add at 0°C is used to convert ice to water and the temperature remains constant until all the ice has melted. Once we reach this point, any further addition of heat causes the temperature of the liquid water to increase. You observed a phase change process for ice (solid water) being melted, heated and then boiled in class. A graph of the temperature of the system versus the amount of heat added (or temp vs time if the heat is added at a constant rate) is called a heating curve. You made a heating curve for water as it melted, then heated then vaporized in LAD 5 and a cooling curve for paradichlorobenzene as it goes through a cooling-freezing-cooling process in LAD 6.
Understand each Segment on the Heating Curve below
AB Heating ice from -15°C to 0°C is represented by the sloping line segment AB Converting the ice at 0°C to water at 0°C is the horizontal segment BC. Additional heat increases the temperature of the water until the temperature reaches 100°C during segment CD. The heat is then used to convert water to steam at a constant temperature of 100°C during segment DE. The steam is then heated to its final temperature of 125°C in the sloping segment EF.
Heating Curve for Water
120 100 temp (ºC) 80 60 40 20 0
F D E
BC
CD
DE
B
C
EF
-20 A
0
5000
10000 15000 20000 25000 30000 35000 heat (Joules)
Energy Calculations for the Sloping Segments of the Heating (or Cooling) Curve
We can calculate the energy change of the system for each of the segments of a heating curve. In segments AB, CD, and EF we are heating a single phase
(pg 1 of 2)
Heating and Cooling Curves
What happens when we heat a sample of ice that is initially at -15°C? The addition of heat causes the temperature of the ice to increase. As long as the temperature is below 0°C, the sample remains frozen. When the temperature reaches 0°C (the melting point of water), the ice begins to melt. Because melting is an endothermic process, the heat we add at 0°C is used to convert ice to water and the temperature remains constant until all the ice has melted. Once we reach this point, any further addition of heat causes the temperature of the liquid water to increase. You observed a phase change process for ice (solid water) being melted, heated and then boiled in class. A graph of the temperature of the system versus the amount of heat added (or temp vs time if the heat is added at a constant rate) is called a heating curve. You made a heating curve for water as it melted, then heated then vaporized in LAD 5 and a cooling curve for paradichlorobenzene as it goes through a cooling-freezing-cooling process in LAD 6.
Understand each Segment on the Heating Curve below
AB Heating ice from -15°C to 0°C is represented by the sloping line segment AB Converting the ice at 0°C to water at 0°C is the horizontal segment BC. Additional heat increases the temperature of the water until the temperature reaches 100°C during segment CD. The heat is then used to convert water to steam at a constant temperature of 100°C during segment DE. The steam is then heated to its final temperature of 125°C in the sloping segment EF.
Heating Curve for Water
120 100 temp (ºC) 80 60 40 20 0
F D E
BC
CD
DE
B
C
EF
-20 A
0
5000
10000 15000 20000 25000 30000 35000 heat (Joules)
Energy Calculations for the Sloping Segments of the Heating (or Cooling) Curve
We can calculate the energy change of the system for each of the segments of a heating curve. In segments AB, CD, and EF we are heating a single phase