TEMPERATURE
Introduction
Temperature is the measure of the average kinetic energy of an object. The energy the object
gets or loses comes from heat. Objects become hotter by adding energy and are cooled by
having energy taken away. Temperature is one way of indicating the amount of energy gained or
lost. Some facts about temperature are:
 Molecules of an object seem to change their motion as the temperature changes,
 A molecule's motion is increased as heat energy is added,
 The same molecule will slow in its motion as this energy is lost or taken away,
 Molecules also have the ability to expand or contract in size. As the amount of heat
energy is added the molecule will grow or expand in size. If that molecule has heat
energy taken away the molecule contracts in size. This is the concept that scientist use
today to measure temperature.
Temperature is measured with a device called a thermometer that measures the temperature
of an object at a specific time. This temperature scale has been set up with "fixed points" to use
for comparison. A German physicist Gabriel Fahrenheit set up the first measurement scale in the
17th century. This is the scale that you still use for everyday measurements in the United States.
This scale was set up by putting 0° F as the coldest possible temperature scientists could reach in
the laboratory at that time. This was achieved by mixing ice, salt, and water -- the same process
you might use to make ice cream. The upper end of his scale was the normal body temperature,
thought, at the time to be 96° F. Today we know this to be 98.6° F. The scale was then divided
into 96 equal spaces or degrees between the two "fixed points" of 0° F & 96° F.
The lower and upper fixed points chosen by Fahrenheit were not very "fixed". They
could not always be reproduced exactly. Thus in the 18th century, Andre Celsius a Swedish
astronomer, proposed a new temperature scale. The Celsius temperature scale had its fixed
points as the temperatures at which water froze as 0° C and boiled as 100° C at normal
atmospheric pressure. The freezing and boiling points of water are true fixed points. They can
be easily reproduced to check a thermometer.
In the 19th century, William Thompson (later knighted Lord Kelvin) proposed yet a
third temperature scale. It was based on Thompson's idea that there could exist an absolute zero
temperature, that temperature at which all molecular motion stops. This scale was called the
Kelvin temperature scale. The Kelvin scale starts at a rock bottom fixed point - absolute zero.
Absolute zero is given the symbol 0 K, which is read as "zero Kelvins." Note that neither the
word "degree" nor the symbol "°" is used. The Kelvin itself is the unit of temperature on the
Kelvin scale. One Kelvin is exactly the same temperature difference as one Celsius degree. This
means that zero Kelvin equals -273° C and likewise, 0° C equals 273 K, or 273 Kelvins. There
is a simple convenience to the Kelvin temperature scale. It has no negative values. After all,
how can there be a temperature lower than absolute zero?
Figure 1 shows the three temperature scales side by side. Notice that the Fahrenheit
degree is smaller than the Celsius degree or the Kelvin measurement. There are 180 Fahrenheit
degrees between the freezing and boiling points of water. There are only 100 Celsius and
Kelvin units in this same range of temperature. Also note that the values for the fixed points on
the Fahrenheit and Celsius scales are different. Water freezes at 0° C or 32° F. Water boils at
100° C or 212° F.
12
The formulas for converting between Fahrenheit and Celsius scales are:
°F = 9/5  (°C) + 32
°C = 5/9  ( °F – 32 )
The formulas really make sense when you stop to think about them. Of course, they still
seem more complicated than the simple relationship between Celsius and Kelvin scales:
K = (°C) + 273
There are two main types of thermometers, each work on the principle of thermal expansion.
The type of thermometer that we will be using in class is a sealed glass tube liquid thermometer.
The liquids most often used in these thermometers are mercury or alcohol. The second type is
called a bimetallic strip thermometer. Inside this type you will find a strip of two metals welded
together. The thermal expansion of one of the metals is greater than that of the other. The strip,
therefore, reacts to temperature changes. When the strip becomes warm the metal with the better
thermal expansion will expand faster and the strip will begin to bend. As the strip cools and the
metals begin to contract the strip will bend back to its original size and shape. Many of your
home thermostats use this type of thermometer.
Figure 1
212º
100º
373
98.6º
37º
310
32º
0º
273
-31º
-35º
238
-273º
0
-460º
FAHRENHEIT
CELSIUS
13
KELVIN
LAB#2-1
Checking Fixed Points on a Thermometer
MATERIALS: thermometer, 400 mL beaker, ring stand, rubber stopper, burette clamp, crushed
ice, hot plate, aprons and safety glasses.
PURPOSE: Write your own. (What should you be able to do at the completion of this lab?)
HYPOTHESIS: Answer these questions before testing takes place:
What is the melting temperature of ice on the Celsius Temperature Scale?
What is the boiling temperature of water using the Celsius scale?
How hot will the water get using the Celsius scale?
INTRODUCTION:
The freezing temperature of water is precisely the same as the melting temperature of ice.
Since it is easier to melt ice than it is to freeze water, you will be finding the temperature at
which ice melts and allowing the water to continue to be heated to its boiling point.
PROCEDURE: Part 1 -- Checking fixed points on a thermometer
Because we will be heating glass you will be expected to be wearing SAFETY GLASSES and an
APRON.
1. Make sure the thermometer set up is securely fixed to the ring stand. Make sure the entire
temperature scale is easily seen (at least between 0° C & 100° C).
2. Fill a 400mL beaker with crushed ice and pour a small amount of water into the beaker.
3. Record the reading of the thermometer in Data Table 1 as Time 0 min. before it is placed in
the ice.
4. Turn on the hot plate to HI.
5. Lower the thermometer into the middle of the crushed ice. After one minute take the
temperature reading and record in Data Table #1. NOTE: Keep ice packed around the bulb
of the thermometer until is no longer possible and then stir the mixture continuously until
boiling. Continue to take readings at one-minute intervals.
6. When the ice melts enough to begin floating in the water, turn the hot plate up as high as it
will go. Continue to stir constantly, and take one-minute readings until the water has boiled
(allow the water to come to a rolling boil and remind boiling for at least five minutes).
7. Turn the hot plate off. Allow the set up to cool before taking it apart - it will be HOT! If
time does not allow, leave the set up together and the next class will take it apart.
PROCEDURE Part 2: Graphing your data
1. Using a full sheet of graph paper make a graph of the data above.
2. Determine the independent and dependent variable from the data you just collected.
3. Find the range of variables for the x & y-axes. Use zero as the starting points for the x-axis
& -2° C for the starting point of the y-axis.
4. Plot the points from your data.
5. Do not connect the points on the graph
6. Title the graph
14
DATA TABLE #1: (Please complete the table below to run for at least 25 minutes)
TIME
TEMPERATURE
0 min
1 min
2 min
3 min
4 min
QUESTIONS
1. What is the standard melting temperature of ice? What is the standard freezing temperature
of water?
2. After placing the thermometer in the ice how long did it take to reach a steady temperature
reading? Why did it remain steady?
3. At what point did you notice the temperature starting to change as the ice melted?
4. According to the data table or the graph what is the melting temperature of the ice? How can
you tell?
5. According to the data table or the graph what is the boiling temperature of water? How can
you tell?
6. According to standard Celsius temperatures what is the boiling point and the freezing point
of water?
7. According to these standards is your thermometer scale accurately marked? How can you
tell?
8. What happens to the heat from the hot plate transmitted to the ice during the melting
process?
9. What happens to the heat from the hot plate transmitted to the water below the boiling
point?
10. What happens to the heat from the hot plate transmitted to the water at the boiling point?
11. Why are two fixed points needed to set up a temperature scale?
12. What would the temperature in Kelvin units be if the temperature was: (this is not multiple
choice!)
i. a. -18°C
b. 14°C
c. 127°C
13. If room temperature on the Fahrenheit scale is 70°F. What is room temperature in the
Celsius scale?
14. Convert 45°C to °F.
ANALYSIS & REFLECTION should include the following:
15