SCIENCE ACTIVITY: HEATING CURVES
(HeatingCurves.docx)
1. Introduction: Water molecules have a strong attraction for one another because they are polar
and they form hydrogen bonds. The polarity of water accounts for its high specific heat and
relatively high enthalpy of fusion and enthalpy of vaporization.
2. Task 1: Use the data in the table on page 2 of this handout and the graph paper provided to
plot a heating curve of temperature versus time for a 180 gram sample of water as it is heated at a
constant rate from -20 degrees C to +120 degrees C.
3. Task 2: Using a ruler, draw five line segments, each being a line of best fit through the points
in each of the five sections of the line you plotted. Note the time required for the water to pass
through each segment of your graph.
4. Task 3: On your own paper, analyze each of the five regions of the graph. Write a short
description of how the heat changes the energy (both kinetic and potential) of the water
molecules in that portion of the heating process.
5. Task 4: On your own paper, calculate the amount of heat required to pass through each
region of the graph. Use these measured values for the properties of water:
180 grams H2O = 10 mol H2O
Hfus = 6.01 kJ / mol
Hvap = 40.7 kJ / mol
cH2O(s) = 2.03 J / (g · °C.)
cH2O(l) = 4.184 J / (g · °C.)
cH2O(g) = 2.01 J / (g · °C.)
6. Task 5: What would the heating curve of ethanol look like? Ethanol melts at -114 degrees C.
and boils at 78 degrees C. Using a second piece of graph paper, sketch the heating curve for
ethanol from -120 degrees C. to 90 degrees C.
7. Task 6: Answer on your own paper: What factors determine the length of the flat regions of
the graph and the slope of the curve between the flat regions?
8. Data for water is on the reverse side of this page.
Data for the Heating Curve of Water
Time (min): Temperature (°C.):
0
-20
1
0
2
0
3
9
4
26
5
42
6
58
7
71
8
83
9
92
10
98
11
100
12
100
13
100
14
100
15
100
16
100
17
100
18
100
19
100
20
100
21
100
22
100
23
100
24
100
25
120
TEACHER NOTES:
Heating Curve of Water
140
120
Temperature (deg C.)
100
80
60
40
20
0
0
5
10
15
-20
-40
Time (minutes)
20
25
30